b43: b43_phyops_a can be static

CC: "Rafał Miłecki" <zajec5@gmail.com>
CC: "John W. Linville" <linville@tuxdriver.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>