staging: media: sun6i-isp: drop of_match_ptr for ID table

The driver can match only via the DT table so the table should be always
used and the of_match_ptr does not make any sense.

This also fixes this !CONFIG_OF error:

drivers/staging/media/sunxi/sun6i-isp/sun6i_isp.c:529:34: warning: 'sun6i_isp_of_match' defined but not used [-Wunused-const-variable=]
  529 | static const struct of_device_id sun6i_isp_of_match[] = {
      |                                  ^~~~~~~~~~~~~~~~~

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>