media: atomisp-gc0310: return errors at gc0310_init()

If something wrong gets there, return the error.

Get rid of this warning:

  drivers/staging/media/atomisp/i2c/atomisp-gc0310.c: In function 'gc0310_init':
  drivers/staging/media/atomisp/i2c/atomisp-gc0310.c:713:6: warning: variable 'ret' set but not used [-Wunused-but-set-variable]
    int ret;
        ^~~

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>