ar71xx: avoid AR71XX_MODEL ending with a space on some TP-LINK-like devices

ar71xx: avoid AR71XX_MODEL ending with a space on some TP-LINK-like devices

Instead of adding the space when combining $model and $hwver, add the space
to the beginning of $hwver, so the resulting string won't end with a space
when $hwver is set to the empty string.

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@49106 3c298f89-4303-0410-b956-a3cf2f4a3e73