V4L/DVB (8742): pvrusb2: use proper byteorder interface

___swab32 is an internal detail of the implementation.

Acked-by: Mike Isely <isely@pobox.com>
Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>