V4L/DVB: gspca - ov534: Fix end of frame handling

Fix a regression, introduced in the driver split, which made
the ov534 driver unusable.
Plus, the debug message should reflect that we discard also packets
beyond the expected frame size.

Signed-off-by: Antonio Ospite <ospite@studenti.unina.it>
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>