kbuild: Fix make rpm

make rpm was broken by commit 0915512:
make clean
set -e; cd ..; ln -sf /usr/src/iwlwifi-2.6 kernel-2.6.35rc4wl
/bin/sh /usr/src/iwlwifi-2.6/scripts/setlocalversion --scm-only >
/usr/src/iwlwifi-2.6/.scmversion
cat: .scmversion: input file is output file
make[1]: *** [rpm] Error 1

Reported-and-tested-by: "Zheng, Jiajia" <jiajia.zheng@intel.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/setlocalversion

@@ -10,13 +10,13 @@
 #
 
 usage() {
-	echo "Usage: $0 [--scm-only] [srctree]" >&2
+	echo "Usage: $0 [--save-scmversion] [srctree]" >&2
 	exit 1
 }
 
 scm_only=false
 srctree=.
-if test "$1" = "--scm-only"; then
+if test "$1" = "--save-scmversion"; then
 	scm_only=true
 	shift
 fi
@@ -132,7 +132,10 @@ collect_files()
 }
 
 if $scm_only; then
-	scm_version
+	if test ! -e .scmversion; then
+		res=$(scm_version)
+		echo "$res" >.scmversion
+	fi
 	exit
 fi