rt2x00: Fix TX status reporting

Not all values of the TX status enumeration were
covered during updating of the TX statistics. This
could lead to wrong bitrate tuning but also wrong
behavior in tools like hostapd.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>