wl1251: fix bssid handling

bssid needs to be copied first in wl1251_op_bss_info_changed(), otherwise
templates will have incorrect bssid and power save will not work
correctly.

Signed-off-by: Kalle Valo <kalle.valo@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>