[media] media-entity.c: get rid of var length arrays

Fix those sparse warnings:
	drivers/media/media-entity.c:238:17: warning: Variable length array is used.
	drivers/media/media-entity.c:239:17: warning: Variable length array is used.

That allows sparse and other code check tools to verify if the
function is using more stack than allowed.

It also solves a bad Kernel pratice of using var length arrays
at the stack.
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/media-entity.c

@@ -235,8 +235,8 @@ __must_check int media_entity_pipeline_start(struct media_entity *entity,
 	media_entity_graph_walk_start(&graph, entity);
 
 	while ((entity = media_entity_graph_walk_next(&graph))) {
-		DECLARE_BITMAP(active, entity->num_pads);
-		DECLARE_BITMAP(has_no_links, entity->num_pads);
+		DECLARE_BITMAP(active, MEDIA_ENTITY_MAX_PADS);
+		DECLARE_BITMAP(has_no_links, MEDIA_ENTITY_MAX_PADS);
 		unsigned int i;
 
 		entity->stream_count++;

include/media/media-entity.h

@@ -116,6 +116,13 @@ static inline u32 media_entity_subtype(struct media_entity *entity)
 #define MEDIA_ENTITY_ENUM_MAX_DEPTH	16
 #define MEDIA_ENTITY_ENUM_MAX_ID	64
 
+/*
+ * The number of pads can't be bigger than the number of entities,
+ * as the worse-case scenario is to have one entity linked up to
+ * MEDIA_ENTITY_ENUM_MAX_ID - 1 entities.
+ */
+#define MEDIA_ENTITY_MAX_PADS		(MEDIA_ENTITY_ENUM_MAX_ID - 1)
+
 struct media_entity_graph {
 	struct {
 		struct media_entity *entity;