vgacon: fix missing include.

This fixes the build error.

Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index 0dd6d962..9d8feac 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -42,6 +42,7 @@
 #include <linux/kd.h>
 #include <linux/slab.h>
 #include <linux/vt_kern.h>
+#include <linux/sched.h>
 #include <linux/selection.h>
 #include <linux/spinlock.h>
 #include <linux/ioport.h>