media: drivers: delete unnecessary variable initialisations

The variables will be set to an appropriate value before usage.
Thus omit the explicit initialisation at the beginning.

[mchehab@s-opensource.com: fold similar patches into one]

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>