kconfig: fix broken target update-po-config

Massimo Maiurana reported:
In the latest kernel "make update-po-config" fails because it tries
to open arch/Kconfig/Kconfig, since the ls command doesn't
distinguish between files and directories.

Cc: Massimo Maiurana <maiurana@gmail.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>

scripts/kconfig/Makefile

@@ -36,10 +36,10 @@ update-po-config: $(obj)/kxgettext $(obj)/gconf.glade.h
 	    --output $(obj)/config.pot
 	$(Q)sed -i s/CHARSET/UTF-8/ $(obj)/config.pot
 	$(Q)ln -fs Kconfig.i386 arch/um/Kconfig.arch
-	$(Q)(for i in `ls arch/`;                        \
+	$(Q)(for i in `ls arch/*/Kconfig`;               \
 	    do                                           \
 		echo "  GEN $$i";                        \
-		$(obj)/kxgettext arch/$$i/Kconfig        \
+		$(obj)/kxgettext $$i                     \
 		     >> $(obj)/config.pot;               \
 	    done )
 	$(Q)msguniq --sort-by-file --to-code=UTF-8 $(obj)/config.pot \