Make the "z/VM unit record device driver" depend on S390

I really don't see anybody else wanting to select it ;)

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/s390/char/Kconfig b/drivers/s390/char/Kconfig
index a3d095d..3f36cb3 100644
--- a/drivers/s390/char/Kconfig
+++ b/drivers/s390/char/Kconfig
@@ -166,6 +166,7 @@
 
 config S390_VMUR
 	tristate "z/VM unit record device driver"
+	depends on S390
 	default "m"
 	help
 	  Character device driver for z/VM reader, puncher and printer.