b43: HT-PHY: move TX fix to the separated function

On N-PHY after B43_PHY_B_TEST operation there is a call to TX power fix
function which iterates over available cores. It matches our HT-PHY code
which means it's probably also some TX fix.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>