[media] cxusb: fix sparse warnings

cxusb.c:1443:32: warning: restricted __le16 degrades to integer
cxusb.c:1487:32: warning: restricted __le16 degrades to integer

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>