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/arch/um/drivers/line.c b/arch/um/drivers/line.c
index 14a102e..cf8a97f 100644
--- a/arch/um/drivers/line.c
+++ b/arch/um/drivers/line.c
@@ -5,6 +5,7 @@
 
 #include "linux/irqreturn.h"
 #include "linux/kd.h"
+#include "linux/sched.h"
 #include "chan_kern.h"
 #include "irq_kern.h"
 #include "irq_user.h"