staging: wfx: drop useless struct hif_pm_mode

Struct hif_pm_mode has no reason to exist. Drop it and simplify access
to struct hif_req_set_pm_mode.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200907101521.66082-17-Jerome.Pouiller@silabs.com


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