kbuild: fix help output to show correct arch

Signed-off-by: NAndres Salomon <dilinger@debian.org>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>

Makefile

@@ -1223,9 +1223,9 @@ help:
 	@echo  'Documentation targets:'
 	@$(MAKE) -f $(srctree)/Documentation/DocBook/Makefile dochelp
 	@echo  ''
-	@echo  'Architecture specific targets ($(ARCH)):'
+	@echo  'Architecture specific targets ($(SRCARCH)):'
 	@$(if $(archhelp),$(archhelp),\
-		echo '  No architecture specific help defined for $(ARCH)')
+		echo '  No architecture specific help defined for $(SRCARCH)')
 	@echo  ''
 	@$(if $(boards), \
 		$(foreach b, $(boards), \