mwl8k: Fixing Sparse ENDIAN CHECK warning

Fixing following sparse warning
>drivers/net/wireless/mwl8k.c:2780:15: warning: incorrect type in assignment (different base types)
>drivers/net/wireless/mwl8k.c:2780:15:    expected restricted unsigned short [usertype] channel
>drivers/net/wireless/mwl8k.c:2780:15:    got unsigned short [unsigned] [usertype] hw_value

Signed-off-by: Yogesh Ashok Powar <yogeshp@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>