staging: vt6656: Remove unused rf_type in channel.c

Remove rf_type that supports 5GHz band.

Signed-off-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
Link: https://lore.kernel.org/r/99af8605af8d348c6b60553c54149ad55da0e3b6.1646935331.git.philipp.g.hortmann@gmail.com


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