Fix a typo in the machine type being extracted from /proc/cpuinfo
which causes all Mikrotik board to be undetected properly.
This lead to sysupgrade issues and probably some others too.
Fixes: 76c963bb01 ("ar71xx: base-files: fix board detect on new MikroTik devices")
Signed-off-by: Koen Vandeputte <koen.vandeputte@ncentric.com>