wifi: mwifiex: fix endianness handling in mwifiex_send_rgpower_table

wifi: mwifiex: fix endianness handling in mwifiex_send_rgpower_table

The length of the host command is a u16 stored in little endian byte
order, which needs byte order conversion to work correctly on big endian
systems.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/linux-wireless/aLqZI4FfOI4iJZtf@stanley.mountain
Fixes: 7b6f16a25806 ("wifi: mwifiex: add rgpower table loading support")
Signed-off-by: Stefan Kerkmann <s.kerkmann@pengutronix.de>
Reviewed-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Link: https://patch.msgid.link/20250910-for-next-v1-1-3ee311706231@pengutronix.de
Signed-off-by: Johannes Berg <johannes.berg@intel.com>