[media] dw9714: Set the v4l2 focus ctrl step as 1

Current v4l2 focus ctrl step value of 16, limits the minimum granularity
of focus positions to 16. Setting this value as 1, enables more accurate
focus positions.

Signed-off-by: Rajmohan Mani <rajmohan.mani@intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>