backend-drm/state-propose: print format instead of *pixel_format_info address

fb->format is *pixel_format_info, whereas fb->format->format is the
actual DRM/wl_shm format code we want to see here. Fix the drm_debug()
call accordingly.

Signed-off-by: Bastian Krause <bst@pengutronix.de>

libweston/backend-drm/state-propose.c

@@ -159,7 +159,7 @@ drm_output_plane_has_valid_format(struct drm_plane *plane,
 		  drm_output_get_plane_type_name(plane),
 		  drm_output_get_plane_type_name(plane),
 		  fb->format->drm_format_name,
-		  (unsigned long) fb->format,
+		  (unsigned long) fb->format->format,
 		  (unsigned long long) fb->modifier);
 
 	return false;