rt2x00: rt2800lib: Fix rx path on SoC devices

Restore the rfcsr initialization for RT305x SoC devices which was removed
by "rt2x00: Finish rt3070 support in rt2800 register initialization.".

This fixes the rx path on SoC devices.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>