[media] usbvision: cleanup the code

[media] usbvision: cleanup the code

There's a dead code on usbvision that makes it harder to read
and produces a smatch warning about bad identation.

Improve the code readability and add a FIXME to warn about
the current hack there.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>