rt2x00: Cleanup/optimize set_state() function callback function

* Reduce goto usage
* Mark if-statements which are true on hardware error unlikely()
* Cleanup debug messages

This makes the code look nicer and be better optimized since
the chance of hardware errors should be very small.

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