wl1271: Fix supported rate management

Previously, only basic rates were used for data transmission - resulting in
reduced transfer rates. This patch takes enables the firmware to take advantage
of the full set of data rates supported by the AP.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>