rt2x00: rt2800lib: no need to toggle RF R30 bit 7 twice

In rt2800_config_channel_rf3xxx(), there's no need to toggle
RF R30 bit 7 twice.

Signed-off-by: Kevin Lo <kevlo@kevlo.org>
Acked-by: Stanislaw Gruszka <stf_xl@wp.pl>
Signed-off-by: John W. Linville <linville@tuxdriver.com>