sysrq: include interrupt.h instead of irq.h

Impact: fix compile error on s390.

With "cpumask: update irq_desc to use cpumask_var_t" in linux-next
we get this compile bug on s390:

  CC      drivers/char/sysrq.o
In file included from drivers/char/sysrq.c:38:
include/linux/irq.h: In function 'init_alloc_desc_masks':
include/linux/irq.h:442: error: dereferencing pointer to incomplete type

Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

drivers/char/sysrq.c

@@ -35,7 +35,7 @@
 #include <linux/vt_kern.h>
 #include <linux/workqueue.h>
 #include <linux/kexec.h>
-#include <linux/irq.h>
+#include <linux/interrupt.h>
 #include <linux/hrtimer.h>
 #include <linux/oom.h>