media: atmel: atmel-isi: properly initialize pad_cfg

In try_fmt, properly initialize the pad_cfg variable to zeros.
This can be used by various calls from the subdev, so it's better
to have it initialized.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
[hverkuil-cisco@xs4all.nl: changed {0} to {}]
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>