staging: wfx: simplify hif_set_tx_rate_retry_policy() usage

staging: wfx: simplify hif_set_tx_rate_retry_policy() usage

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

So, this patch relocate handling of this structure to
hif_set_tx_rate_retry_policy() (the low level function).

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200115135338.14374-6-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>