[media] em28xx: add a missing le16_to_cpu conversion

commit 61ff5d69 "em28xx: improve em2710/em2820 distinction" missed the
le16_to_cpu conversion of the USB vendor ID.

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>