staging: wfx: field operational_rate_set is ignored by firmware

The field bss_params.operational_rate_set is ignore by the firmware. It
is not necessary to send it. This change greatly simplify
wfx_join_finalize(). It is no more necessary to get sta and it allow to
save a RCU.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200420160311.57323-8-Jerome.Pouiller@silabs.com


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