opp: rust: mark OPP methods as inline

When building the kernel using llvm-19.1.7-rust-1.85.0-x86_64, the
following symbols are generated:

$ nm vmlinux | grep ' _R'.*OPP | rustfilt
ffffffff81801560 T <kernel::opp::OPP>::freq
ffffffff81801540 T <kernel::opp::OPP as kernel::sync::aref::AlwaysRefCounted>::dec_ref
ffffffff81801520 T <kernel::opp::OPP as kernel::sync::aref::AlwaysRefCounted>::inc_ref

However, these Rust symbols are trivial wrappers around the
`dev_pm_opp_get`, `dev_pm_opp_put` and `dev_pm_opp_get_freq_indexed`
functions. It doesn't make sense to go through a trivial wrapper for
these functions.

After applying this patch, the above command will produce no output.

Link: https://github.com/Rust-for-Linux/linux/issues/1145
Suggested-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Nicolás Antinori <nico.antinori.7@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

rust/kernel/opp.rs

@@ -1042,11 +1042,13 @@ unsafe impl Sync for OPP {}
 
 /// SAFETY: The type invariants guarantee that [`OPP`] is always refcounted.
 unsafe impl AlwaysRefCounted for OPP {
+    #[inline]
     fn inc_ref(&self) {
         // SAFETY: The existence of a shared reference means that the refcount is nonzero.
         unsafe { bindings::dev_pm_opp_get(self.0.get()) };
     }
 
+    #[inline]
     unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
         // SAFETY: The safety requirements guarantee that the refcount is nonzero.
         unsafe { bindings::dev_pm_opp_put(obj.cast().as_ptr()) }
@@ -1095,6 +1097,7 @@ fn as_raw(&self) -> *mut bindings::dev_pm_opp {
     }
 
     /// Returns the frequency of an [`OPP`].
+    #[inline]
     pub fn freq(&self, index: Option<u32>) -> Hertz {
         let index = index.unwrap_or(0);