rt2x00: rt2800lib: no need to write RF register 3 twice for RT5592

In rt2800_init_rfcsr_5592(), there's no need to write RF register 3 twice.

Signed-off-by: Kevin Lo <kevlo@kevlo.org>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>