drm/xe: fix refcount leak in xe_range_fence_insert()

xe_range_fence_insert() acquires a reference on fence via
dma_fence_get() and stores it in rfence->fence.  It then calls
dma_fence_add_callback() and handles two cases: when the callback
is successfully registered (err == 0) the fence is transferred to
the tree for later cleanup; when the fence is already signaled
(err == -ENOENT) it manually drops the extra reference with
dma_fence_put(fence).

However, dma_fence_add_callback() can fail with other errors
(e.g. -EINVAL) and in that case the code falls through to the free:
label without releasing the acquired reference, leaking it.

Fix the leak by adding an else branch that calls dma_fence_put()
before jumping to free: for any error other than -ENOENT.

Fixes: 845f64bdbf ("drm/xe: Introduce a range-fence utility")
Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260610172705.3450560-1-matthew.brost@intel.com
(cherry picked from commit 98c4a4201290823c2c5c7ba21692bd9a64b61021)
Signed-off-by: Matthew Brost <matthew.brost@intel.com>

drivers/gpu/drm/xe/xe_range_fence.c

@@ -77,6 +77,8 @@ int xe_range_fence_insert(struct xe_range_fence_tree *tree,
 	} else if (err == 0) {
 		xe_range_fence_tree_insert(rfence, &tree->root);
 		return 0;
+	} else {
+		dma_fence_put(fence);
 	}
 
 free: