mwifiex: fix sparse warning

This patch fixes following sparse warnings:

drivers/net/wireless/mwifiex/util.c:152:19: warning: cast from restricted __le16
drivers/net/wireless/mwifiex/util.c:152:19: warning: restricted __le16 degrades to integer

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>