[media] gspca - main: Fix a regression with the PS3 Eye webcam

When audio is present, some alternate settings were skipped.
This prevented some webcams to work, especially when bulk transfer was used.
This patch permits to use the last or only alternate setting.

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