wifi: mwifiex: use MODULE_FIRMWARE to add firmware files metadata

The mwifiex_pcie driver is missing the MODULE_FIRMWARE macro to
add the firmware files needed to the module metadata.

Signed-off-by: Víctor Gonzalo <victor.gonzalo@anddroptable.net>
Acked-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230914211938.28395-1-victor.gonzalo@anddroptable.net