V4L/DVB: dvb_ca_en50221: return -EFAULT on copy_to_user errors

copy_to_user() returns the number of bytes remaining to be copied which
isn't the right thing to return here.  The comments say that these
functions in dvb_ca_en50221.c should return the number of bytes copied or
an error return.  I've changed it to return -EFAULT.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>