wl1271: Remove tx-power level workaround

This patch removes the workaround limiting chipset TX power to 12dB, instead
using the value configured by the mac80211.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Teemu Paasikivi <ext-teemu.3.paasikivi@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>