staging: vt6556: vnt_rf_setpower convert to use ieee80211_channel.

ieee80211_channel contains all the necessary information to change
power according to tx mode required.

vnt_rf_setpower is moved and so that vnt_rf_set_txpower the only
caller becomes static.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Link: https://lore.kernel.org/r/9eab9af8-fde9-1dc6-fced-95c7a36ecc01@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>