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/include/asm/setup.h b/arch/s390/include/asm/setup.h
index 908f688..87b47ca 100644
--- a/arch/s390/include/asm/setup.h
+++ b/arch/s390/include/asm/setup.h
@@ -60,7 +60,7 @@
 #define SECONDARY_SPACE_MODE	2
 #define HOME_SPACE_MODE		3
 
-extern unsigned int addressing_mode;
+extern unsigned int s390_user_mode;
 
 /*
  * Machine features detected in head.S