drm/mm: Mark drm_mm_interval_tree*() functions with __maybe_unused

[ Upstream commit 53bd7c1c0077db533472ae32799157758302ef48 ]

The INTERVAL_TREE_DEFINE() uncoditionally provides a bunch of helper
functions which in some cases may be not used. This, in particular,
prevents kernel builds with clang, `make W=1` and CONFIG_WERROR=y:

.../drm/drm_mm.c:152:1: error: unused function 'drm_mm_interval_tree_insert' [-Werror,-Wunused-function]
  152 | INTERVAL_TREE_DEFINE(struct drm_mm_node, rb,
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  153 |                      u64, __subtree_last,
      |                      ~~~~~~~~~~~~~~~~~~~~
  154 |                      START, LAST, static inline, drm_mm_interval_tree)
      |                      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fix this by marking drm_mm_interval_tree*() functions with __maybe_unused.

See also commit 6863f56 ("kbuild: allow Clang to find unused static
inline functions for W=1 build").

Fixes: 202b52b ("drm: Track drm_mm nodes with an interval tree")
Signed-off-by: Andy Shevchenko <[email protected]>
Reviewed-by: Jani Nikula <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Signed-off-by: Jani Nikula <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

drivers/gpu/drm/drm_mm.c

@@ -154,7 +154,7 @@ static void show_leaks(struct drm_mm *mm) { }
 
 INTERVAL_TREE_DEFINE(struct drm_mm_node, rb,
 		     u64, __subtree_last,
-		     START, LAST, static inline, drm_mm_interval_tree)
+		     START, LAST, static inline __maybe_unused, drm_mm_interval_tree)
 
 struct drm_mm_node *
 __drm_mm_interval_first(const struct drm_mm *mm, u64 start, u64 last)