s390/crashdump: remove unused variable

Get rid of this compile warning:

arch/s390/kernel/crash_dump.c: In function 'copy_from_realmem':
arch/s390/kernel/crash_dump.c:48:6: warning: unused variable 'rc'
[-Wunused-variable]
int rc;
^

Signed-off-by: Heiko Carstens <[e-mail]>
Signed-off-by: Martin Schwidefsky <[e-mail]>

arch/s390/kernel/crash_dump.c

···
 static int copy_from_realmem(void *dest, void *src, size_t count)
 {
 	unsigned long size;
-	int rc;
 
 	if (!count)
 		return 0;