kbuild: Fix make rpm

make rpm was broken by commit 09155120:
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>