[media] dvb_frontend: Fix __user namespace

As reported by smatch:

drivers/media/dvb-core/dvb_frontend.c:1960:45: warning: incorrect type in argument 2 (different address spaces)
drivers/media/dvb-core/dvb_frontend.c:1960:45:    expected void const [noderef] <asn:1>*from
drivers/media/dvb-core/dvb_frontend.c:1960:45:    got struct dtv_property *[noderef] <asn:1>props
drivers/media/dvb-core/dvb_frontend.c:1992:45: warning: incorrect type in argument 2 (different address spaces)
drivers/media/dvb-core/dvb_frontend.c:1992:45:    expected void const [noderef] <asn:1>*from
drivers/media/dvb-core/dvb_frontend.c:1992:45:    got struct dtv_property *[noderef] <asn:1>props
drivers/media/dvb-core/dvb_frontend.c:2014:38: warning: incorrect type in argument 1 (different address spaces)
drivers/media/dvb-core/dvb_frontend.c:2014:38:    expected void [noderef] <asn:1>*to
drivers/media/dvb-core/dvb_frontend.c:2014:38:    got struct dtv_property *[noderef] <asn:1>props
drivers/media/dvb-core/dvb_frontend.c:1946:17: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:1947:17: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:1951:22: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:1951:42: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:1954:31: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:1960:41: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:1960:54: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:1965:33: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:1978:17: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:1979:17: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:1983:22: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:1983:42: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:1986:31: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:1992:41: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:1992:54: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:2007:33: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:2014:34: warning: dereference of noderef expression
drivers/media/dvb-core/dvb_frontend.c:2014:52: warning: dereference of noderef expression

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>