rt2x00: use rt2800_config_channel_rt3x for rt2872

rt2872 needs the same rf register setup as rt3070 and rt3090, hence
use rt2800_config_channel_rt3x instead of rt2800_config_channel_rt2x.
This change allows me to actually switch channels and hence scan all
configured channels on the RT305x SoC platform (which uses a rt2872)
here.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Tested-by: Luis Correia <luis.f.correia@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>