wl1271: Corrections to TX path

Corrections to the TX path - use correct number of maximum descriptors
(32 instead of 16) and correct checking and setting of excessive retries
on completion.

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>