V4L/DVB (6238): bw-qcam: use data_reverse instead of manually poking the control register

Fixes use of parport_write_control() to match the newer interface that
requires explicit parport_data_reverse() and parport_data_forward() calls.
This eliminates the following error message and restores the original
intended behavior:

parport0 (bw-qcam): use data_reverse for this!

Also increases threshold in qc_detect() from 300 to 400, as my camera often
results in a count of approx 330.  Added a kernel error message to indicate
detection failure.

Thanks Ray and Randy for your comments, and for pointing out that I
needed to reset the port to forward mode!

Signed-off-by: Brett T. Warden <brett.warden@gmail.com>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>