rt2800usb:fix hang during firmware load

The device 057c:8501 (AVM Fritz! WLAN v2 rev. B) boots into a state that does
not actually require loading a firmware file. The vendors driver finds out
about this by checking a firmware state register, so this patch adds this here.

Finally, with this patch applied, my wifi dongle actually becomes
useful (scan + connect to wpa network works).

Signed-off-by: Michael Braun <michael-dev@fami-braun.de>
Acked-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>