staging: wfx: simplify hif_scan() usage

staging: wfx: simplify hif_scan() usage

The structures hif_req_start_scan and hif_ssid_def come from hardware
API. It is not intended to be manipulated in upper layers of the driver.

So, this patch relocate handling of theses structures to hif_scan()
(the low level function). This change also allows to drop struct
wfx_scan_params.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20191217161318.31402-48-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>