drm/i915/fence: replace BUG_ON() with BUILD_BUG_ON()

Avoid BUG_ON(). Since __i915_sw_fence_init() is always called via a
wrapper macro, we can replace it with a compile time BUILD_BUG_ON().
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220830093411.1511040-5-jani.nikula@intel.com

drivers/gpu/drm/i915/i915_sw_fence.c

@@ -241,8 +241,6 @@ void __i915_sw_fence_init(struct i915_sw_fence *fence,
 			  const char *name,
 			  struct lock_class_key *key)
 {
-	BUG_ON(!fn);
-
 	__init_waitqueue_head(&fence->wait, name, key);
 	fence->fn = fn;
 #ifdef CONFIG_DRM_I915_SW_FENCE_CHECK_DAG

drivers/gpu/drm/i915/i915_sw_fence.h

@@ -48,11 +48,15 @@ void __i915_sw_fence_init(struct i915_sw_fence *fence,
 do {								\
 	static struct lock_class_key __key;			\
 								\
+	BUILD_BUG_ON((fn) == NULL);				\
 	__i915_sw_fence_init((fence), (fn), #fence, &__key);	\
 } while (0)
 #else
 #define i915_sw_fence_init(fence, fn)				\
-	__i915_sw_fence_init((fence), (fn), NULL, NULL)
+do {								\
+	BUILD_BUG_ON((fn) == NULL);				\
+	__i915_sw_fence_init((fence), (fn), NULL, NULL);	\
+} while (0)
 #endif
 
 void i915_sw_fence_reinit(struct i915_sw_fence *fence);