[media] videobuf2: fix sparse warning

Fix "symbol 'vb2_vmalloc_memops' was not declared. Should it be static?"
sparse warning.

Signed-off-by: Nicolas Thery <nicolas.thery@st.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/videobuf2-vmalloc.c

@@ -18,6 +18,7 @@
 #include <linux/vmalloc.h>
 
 #include <media/videobuf2-core.h>
+#include <media/videobuf2-vmalloc.h>
 #include <media/videobuf2-memops.h>
 
 struct vb2_vmalloc_buf {