[media] v4l: add g_dv_preset callback to V4L2 subdev

Callback is used to acquire current digital video preset from a subdev.
It is used to avoid keeping dv preset in top-level driver.
Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

include/media/v4l2-subdev.h

@@ -246,6 +246,8 @@ struct v4l2_subdev_audio_ops {
    s_dv_preset: set dv (Digital Video) preset in the sub device. Similar to
 	s_std()
 
+   g_dv_preset: get current dv (Digital Video) preset in the sub device.
+
    query_dv_preset: query dv preset in the sub device. This is similar to
 	querystd()
 
@@ -286,6 +288,8 @@ struct v4l2_subdev_video_ops {
 			struct v4l2_dv_enum_preset *preset);
 	int (*s_dv_preset)(struct v4l2_subdev *sd,
 			struct v4l2_dv_preset *preset);
+	int (*g_dv_preset)(struct v4l2_subdev *sd,
+			struct v4l2_dv_preset *preset);
 	int (*query_dv_preset)(struct v4l2_subdev *sd,
 			struct v4l2_dv_preset *preset);
 	int (*s_dv_timings)(struct v4l2_subdev *sd,