V4L/DVB (6261): Cleans mem->vmalloc after vfree

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>
diff --git a/drivers/media/video/videobuf-vmalloc.c b/drivers/media/video/videobuf-vmalloc.c
index 993d528..6ef4f52 100644
--- a/drivers/media/video/videobuf-vmalloc.c
+++ b/drivers/media/video/videobuf-vmalloc.c
@@ -372,6 +372,7 @@
 	MAGIC_CHECK(mem->magic,MAGIC_VMAL_MEM);
 
 	vfree(mem->vmalloc);
+	mem->vmalloc=NULL;
 
 	return;
 }