s390: add missing declarations

arch_dup_task_struct and the per cpu variable mt_cycles are globally
visible, but do not have any header file with a declaration.
Therefore add it so we have proper type checking in place.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/vtime.c

@@ -18,6 +18,8 @@
 #include <asm/cpu_mf.h>
 #include <asm/smp.h>
 
+#include "entry.h"
+
 static void virt_timer_expire(void);
 
 static LIST_HEAD(virt_timer_list);