contrib: push_pkg: fix lint issues with shellcheck 0.7.1

0.7.1 complains about unescaped backslashes in double quotes (which are
intepreted by printf in the two affected places). While the warning was
retired with shellcheck 0.7.2, it seems like a good idea to fix it
anyways.

contrib/push_pkg.sh

@@ -48,7 +48,7 @@ shift $(( OPTIND - 1 ))
 if [ "$build_only" -eq 0 ]; then
 	remote_info=$(ssh -p "${ssh_port}" "root@${ssh_host}" '
 		source /etc/os-release
-		printf "%s\t%s\n" "$OPENWRT_BOARD" "$OPENWRT_ARCH"
+		printf "%s\\t%s\\n" "$OPENWRT_BOARD" "$OPENWRT_ARCH"
 	')
 	REMOTE_OPENWRT_BOARD="$(echo "$remote_info" | cut -f 1)"
 	REMOTE_OPENWRT_ARCH="$(echo "$remote_info" | cut -f 2)"
@@ -92,7 +92,7 @@ while [ $# -gt 0 ]; do
 	opkg_packages="$(make TOPDIR="${topdir}" -C "${pkgdir}" DUMP=1 | awk '/^Package: / { print $2 }')"
 
 	search_package() {
-		find "$2" -name "$1_*.ipk" -printf "%f\n"
+		find "$2" -name "$1_*.ipk" -printf '%f\n'
 	}
 
 	make TOPDIR="${topdir}" -C "${pkgdir}" clean