rust: kernel: mark as #[inline] all From::from()s for Error

There was a recent request [1] to mark as `#[inline]` the simple
`From::from()` functions implemented for `Error`.

Thus mark all of the existing

    impl From<...> for Error {
        fn from(err: ...) -> Self {
            ...
        }
    }

functions in the `kernel` crate as `#[inline]`.

Suggested-by: Gary Guo <gary@garyguo.net>
Link: https://lore.kernel.org/all/8403c8b7a832b5274743816eb77abfa4@garyguo.net/ [1]
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Acked-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://patch.msgid.link/20260326020406.1438210-1-alistair.francis@wdc.com
[ Dropped `projection.rs` since it is in another tree and already marked
  as `inline(always)` and reworded accordingly. Changed Link tag to
  Gary's original message and added Suggested-by. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust/kernel/alloc/kvec/errors.rs

@@ -15,6 +15,7 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 }
 
 impl<T> From<PushError<T>> for Error {
+    #[inline]
     fn from(_: PushError<T>) -> Error {
         // Returning ENOMEM isn't appropriate because the system is not out of memory. The vector
         // is just full and we are refusing to resize it.
@@ -32,6 +33,7 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 }
 
 impl From<RemoveError> for Error {
+    #[inline]
     fn from(_: RemoveError) -> Error {
         EINVAL
     }
@@ -55,6 +57,7 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 }
 
 impl<T> From<InsertError<T>> for Error {
+    #[inline]
     fn from(_: InsertError<T>) -> Error {
         EINVAL
     }

rust/kernel/error.rs

@@ -216,36 +216,42 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 }
 
 impl From<AllocError> for Error {
+    #[inline]
     fn from(_: AllocError) -> Error {
         code::ENOMEM
     }
 }
 
 impl From<TryFromIntError> for Error {
+    #[inline]
     fn from(_: TryFromIntError) -> Error {
         code::EINVAL
     }
 }
 
 impl From<Utf8Error> for Error {
+    #[inline]
     fn from(_: Utf8Error) -> Error {
         code::EINVAL
     }
 }
 
 impl From<LayoutError> for Error {
+    #[inline]
     fn from(_: LayoutError) -> Error {
         code::ENOMEM
     }
 }
 
 impl From<fmt::Error> for Error {
+    #[inline]
     fn from(_: fmt::Error) -> Error {
         code::EINVAL
     }
 }
 
 impl From<core::convert::Infallible> for Error {
+    #[inline]
     fn from(e: core::convert::Infallible) -> Error {
         match e {}
     }

rust/kernel/xarray.rs

@@ -172,6 +172,7 @@ pub struct StoreError<T> {
 }
 
 impl<T> From<StoreError<T>> for Error {
+    #[inline]
     fn from(value: StoreError<T>) -> Self {
         value.error
     }