menuconfig: let make not report error when not save configuration

I find every time when I choice the 'NO' button at the dialog
which let me choice whether to save the configuration before exit
menuconfig, it always report the blow:

" GEN     /mnt/sda7/home/build/test/Makefile
  HOSTCC  scripts/kconfig/mconf.o
  HOSTLD  scripts/kconfig/mconf
scripts/kconfig/mconf Kconfig

Your configuration changes were NOT saved.

make[2]: *** [menuconfig] Error 1
make[1]: *** [menuconfig] Error 2
make: *** [sub-make] Error 2 "

This patch repair it.

Signed-off-by: Wang YanQing <udknight@gmail.com>
Acked-by: Davidlohr Bueso <dave@gnu.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>