staging: wfx: simplify hif_join()

The structure hif_req_join come from hardware API. It is not intended
to be manipulated in upper layers of the driver.

In add, current code for hif_join() is too dumb. It should pack data
with hardware representation instead of leaving all work to the caller.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200115135338.14374-30-Jerome.Pouiller@silabs.com


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