headers: remove sched.h from interrupt.h

After m68k's task_thread_info() doesn't refer to current,
it's possible to remove sched.h from interrupt.h and not break m68k!
Many thanks to Heiko Carstens for allowing this.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
diff --git a/drivers/char/rio/riotty.c b/drivers/char/rio/riotty.c
index 2fb49e8..47fab7c 100644
--- a/drivers/char/rio/riotty.c
+++ b/drivers/char/rio/riotty.c
@@ -33,6 +33,7 @@
 #define __EXPLICIT_DEF_H__
 
 #include <linux/module.h>
+#include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/errno.h>
 #include <linux/tty.h>