init.sh: add error check on mkdir in gentoo check

yes. i should have reviewed that patch properly.

the code should meet lbmk standards now.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/init.sh

@@ -97,7 +97,7 @@ xbmkpkg()
 		printf "Writing into %s" "$pkg_use_file..."
 
 		if [ ! -d "`dirname $pkg_use_file`" ]; then
-			mkdir -p "`dirname $pkg_use_file`"
+			x_ mkdir -p "`dirname $pkg_use_file`"
 		fi
 
 		printf "%s\n" "$pkg_use" >> "$pkg_use_file"