mwifiex: fix for unaligned reads

Using the accessor function e.g. get_unaligned_le32 instead of
le32_to_cpu to avoid the unaligned access. This is for the
architectures that don't handle the unaligned memory access

Signed-off-by: Devidas Puranik <devidas@marvell.com>
Signed-off-by: Ganapathi Bhat <gbhat@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>