media: atomisp: set per-device's default mode

The atomisp driver originally used the s_parm command to
initialize the run_mode type to the driver. So, before start
setting up the streaming, s_parm should be called.

So, even having 5 "normal" video devices, one meant to be used
for each type, the run_mode was actually selected when
s_parm is called.

Without setting the run mode, applications that don't call
VIDIOC_SET_PARM with a custom atomisp parameters won't work, as
the pipeline won't be set:

	atomisp-isp2 0000:00:03.0: can't create streams
	atomisp-isp2 0000:00:03.0: __get_frame_info 1600x1200 (padded to 0) returned -22

However, commit 8a7c5594 ("media: v4l2-ioctl: clear fields in s_parm")
broke support for it, with a good reason, as drivers shoudn't be
extending the API for their own purposes.

So, as an step to allow generic apps to use this driver, put
the device's run_mode in preview after open.

After this patch, using v4l2grab starts to work on preview
mode (/dev/video2):

	$ v4l2grab -f YUYV -x 1600 -y 1200 -d /dev/video2 -n 1 -u
	$ feh out000.pnm

So, let's just setup the default run_mode that each video devnode
should assume, setting it at open() time.

Reported-by: Tsuchiya Yuto <kitakar@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>