s390/mm: rename addressing_mode to s390_user_mode

Renaming the globally visible variable "user_mode" to "addressing_mode" in
order to fix a name clash was not a good idea. (Commit 37fe1d73 "s390/mm:
rename user_mode variable to addressing_mode")
Looking at the code after a couple of weeks one thinks: addressing mode of
what?
So rename the variable again. This time to s390_user_mode. Which hopefully
makes more sense.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 12c887b..8b2cac1 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -111,7 +111,7 @@
 	if (trans_exc_code == 2)
 		/* Access via secondary space, set_fs setting decides */
 		return current->thread.mm_segment.ar4;
-	if (addressing_mode == HOME_SPACE_MODE)
+	if (s390_user_mode == HOME_SPACE_MODE)
 		/* User space if the access has been done via home space. */
 		return trans_exc_code == 3;
 	/*