mwifiex: check revision id while choosing PCIe firmware

Some of the chipsets have two revisions. This patch
selects appropriate firmware by checking revision id.

Signed-off-by: Shengzhen Li <szli@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>