rt2x00: remove unneeded check

Remove band check from rf53xx channel config routine since all chips
using it are single band.

Signed-off-by: Tomislav Požega <pozega.tomislav@gmail.com>
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>