ar71xx: typo in detect TL-MR10U/TL-MR11U

At offset 0x40, signature for TL-MR10U/TL-MR11U begin
from 0x00, not 0x10/0x11.

Signed-off-by: Cezary Jackiewicz <cezary.jackiewicz@gmail.com>
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

SVN-Revision: 36727