media: sun6i-isp: proc: Declare subdev ops as static

The static keyword is missing in the v4l2 subdev ops definition for the
proc.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Fixes: e3185e1d ("media: staging: media: Add support for the Allwinner A31 ISP")
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>