ath9k: ar5008_hw_cmn_spur_mitigate: add missing mask_m & mask_p initialisation

ath9k: ar5008_hw_cmn_spur_mitigate: add missing mask_m & mask_p initialisation

commit de478a61389cacafe94dc8b035081b681b878f9d upstream.

by moving common code to ar5008_hw_cmn_spur_mitigate i forgot to move
mask_m & mask_p initialisation. This coused a performance regression
on ar9281.

Fixes: f911085ffa88 ("ath9k: split ar5008_hw_spur_mitigate and reuse common code in ar9002_hw_spur_mitigate.")
Reported-by: Gustav Frederiksen <lkml2017@openmailbox.org>
Tested-by: Gustav Frederiksen <lkml2017@openmailbox.org>
Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>