media: mtk-jpeg: remove redundant initialization of variable plane_fmt

The variable plane_fmt is being initialized with a value that is never
read, it is being re-assigned a new value on each iteration of a for
loop. The initialization is redundant and can be removed.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>