wifi: wl18xx: add some missing endian conversions

This caused sparse warnings, and clearly is needed per
how other firmware interfaces behave.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220904212910.2b5cb713cf4b.Ibabba2deb7bb22863d3a134e7a3333422d7eff17@changeid