staging: vt6656: Remove unused rf_type in rf.c; top level

Remove rf_type that supports 5GHz band.

To keep a better overview this is only the first part of the patch.
Compiler Warings about unused variables will be removed with the following
patch.

Signed-off-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
Link: https://lore.kernel.org/r/e111923dffc4781cf9d4e7966c9f365beb93c5ee.1646935331.git.philipp.g.hortmann@gmail.com


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