drm/xe: avoid function cast warnings

clang-16 warns about a cast between incompatible function types:

drivers/gpu/drm/xe/xe_range_fence.c:155:10: error: cast from 'void (*)(const void *)' to 'void (*)(struct xe_range_fence *)' converts to incompatible function type [-Werror,-Wcast-function-type-strict]
  155 |         .free = (void (*)(struct xe_range_fence *rfence)) kfree,
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Avoid this with a trivial helper function that calls kfree() here.

v2:
- s/* rfence/*rfence/ (Thomas)

Fixes: 845f64bd ("drm/xe: Introduce a range-fence utility")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240213095719.454865-1-arnd@kernel.org

drivers/gpu/drm/xe/xe_range_fence.c

@@ -151,6 +151,11 @@ xe_range_fence_tree_next(struct xe_range_fence *rfence, u64 start, u64 last)
 	return xe_range_fence_tree_iter_next(rfence, start, last);
 }
 
+static void xe_range_fence_free(struct xe_range_fence *rfence)
+{
+	kfree(rfence);
+}
+
 const struct xe_range_fence_ops xe_range_fence_kfree_ops = {
-	.free = (void (*)(struct xe_range_fence *rfence)) kfree,
+	.free = xe_range_fence_free,
 };