merge_config.sh: Display usage if given too few arguments

Two or more arguments are always expected. Show usage and exit if
given less.
Signed-off-by: NOlof Johansson <olof@lixom.net>
Signed-off-by: NMichal Marek <mmarek@suse.cz>

scripts/kconfig/merge_config.sh

@@ -77,6 +77,11 @@ while true; do
 	esac
 done
 
+if [ "$#" -lt 2 ] ; then
+	usage
+	exit
+fi
+
 INITFILE=$1
 shift;