mwifiex: Fixed endianness problem for big endian platform

The driver sends and recives information to and from the firmware.
Correct endianness should be ensured as firmware follows little
endian format and host can be little/big endian.

Signed-off-by: Karthik D A <karthida@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>