V4L/DVB (7938): pvrusb2: Increase enforced encoder wait delay to improve reliability

The driver enforces a "quiet period" on the encoder in certain
situations before attempting to operate it.  This seems to help avoid
video encoding errors / corruption.  The quiet period was 50msec, but
through experimentation it has been observed to improve further if the
interval is increased to 100msec.

Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>