ath5k: fix regression which triggers an SME join upon assoc
This fixes a regression introduced by patch titled:
"atheros: define shared bssidmask setting"
The register for the BSSID was exchanged for the bssid mask register.
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>