vgacon: fix missing include.

This fixes the build error.
Signed-off-by: Dave Airlie <airlied@redhat.com>

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>