kconfig: fix another bug of "make savedefconfig"

In some cases, the last lines of SPL or TPL are not output to a file.
The entries remaining in the "unmatched" variable must be flushed.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>

scripts/multiconfig.sh

@@ -229,6 +229,8 @@ do_savedefconfig () {
 				unmatched="$unmatched%$symbol:$line"
 			fi
 		done < defconfig
+
+		output_lines="$output_lines%$unmatched"
 	done
 
 	rm -f defconfig