[media] vivid: add missing includes

Fix kbuild test robot warnings about missing vmalloc.h and string.h
includes.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
diff --git a/drivers/media/platform/vivid/vivid-tpg.h b/drivers/media/platform/vivid/vivid-tpg.h
index 51ef7d1..8ef3e52 100644
--- a/drivers/media/platform/vivid/vivid-tpg.h
+++ b/drivers/media/platform/vivid/vivid-tpg.h
@@ -25,6 +25,7 @@
 #include <linux/errno.h>
 #include <linux/random.h>
 #include <linux/slab.h>
+#include <linux/vmalloc.h>
 #include <linux/videodev2.h>
 
 #include "vivid-tpg-colors.h"