media: staging: atomisp: Disable custom format for now

Custom video format 'M101' is not supported in upstream and as a result
user will get ugly warning:

 Unknown pixelformat 0x3130314d
 ------------[ cut here ]------------
 WARNING: CPU: 3 PID: 1574 at drivers/media/v4l2-core/v4l2-ioctl.c:1291 v4l_enum_fmt+0xcf1/0x13a0 [videodev]

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>