media: staging: media: atomisp: init high & low vars

Fix a compiler warning:

include/linux/dev_printk.h: In function 'ov2680_probe':
include/linux/dev_printk.h:144:31: warning: 'high' may be used uninitialized [-Wmaybe-uninitialized]
  144 |         dev_printk_index_wrap(_dev_err, KERN_ERR, dev, dev_fmt(fmt), ##__VA_ARGS__)
      |                               ^~~~~~~~
In function 'ov2680_detect',
    inlined from 'ov2680_s_config' at drivers/staging/media/atomisp/i2c/atomisp-ov2680.c:468:8,
    inlined from 'ov2680_probe' at drivers/staging/media/atomisp/i2c/atomisp-ov2680.c:647:8:
drivers/staging/media/atomisp/i2c/atomisp-ov2680.c:376:13: note: 'high' was declared here
  376 |         u32 high, low;
      |             ^~~~

'high' is indeed uninitialized after the ov_read_reg8() call failed, so there is no
point showing the value. Just say that the read failed. But low can also be used
uninitialized later, so just make it more robust and properly zero the high and low
variables.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>