[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>

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;