staging: wlan-ng: reduce type warnings

Fixes the following sparse output:

drivers/staging/wlan-ng/p80211conv.c:132:25: warning: cast to restricted __be16
drivers/staging/wlan-ng/p80211conv.c:132:25: warning: cast to restricted __be16
drivers/staging/wlan-ng/p80211conv.c:132:25: warning: cast to restricted __be16
drivers/staging/wlan-ng/p80211conv.c:132:25: warning: cast to restricted __be16
drivers/staging/wlan-ng/p80211conv.c:154:38: warning: incorrect type in assignment (different base types)
drivers/staging/wlan-ng/p80211conv.c:154:38:    expected unsigned short [unsigned] [usertype] type
drivers/staging/wlan-ng/p80211conv.c:154:38:    got restricted __be16 [usertype] <noident>
drivers/staging/wlan-ng/p80211conv.c:390:42: warning: cast to restricted __le16
drivers/staging/wlan-ng/p80211conv.c:413:29: warning: incorrect type in assignment (different base types)
drivers/staging/wlan-ng/p80211conv.c:413:29:    expected unsigned short [unsigned] [usertype] type
drivers/staging/wlan-ng/p80211conv.c:413:29:    got restricted __be16 [usertype] <noident>
drivers/staging/wlan-ng/p80211conv.c:481:29: warning: incorrect type in assignment (different base types)
drivers/staging/wlan-ng/p80211conv.c:481:29:    expected unsigned short [unsigned] [usertype] type
drivers/staging/wlan-ng/p80211conv.c:481:29:    got restricted __be16 [usertype] <noident>

Signed-off-by: Alexander Alemayhu <alexander@alemayhu.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>