ath5k: Always write tx powertable on hw

 * By skipping tx power table calibration we also skip setting
 tx power table on hw. Make sure we always write tx power table
 on hw since it gets cleared on reset.

Signed-off-by: Nick Kossifidis <mickflemm@gmail.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>