V4L/DVB (10945): pwc : fix LED and power setup for first open

Call pwc_construct before trying to talk to device to obtain vc interface so
that LED and power setup works the first time the video device is opened.

Signed-off-by: Martin Fuzzey <mfuzzey@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>