sys/v4l2/gstv4l2src.c: Use define here.

sys/v4l2/gstv4l2src.c: Use define here.

Original commit message from CVS:
Patch by: Alexander Eichner <alexeichi@yahoo.de>
* sys/v4l2/gstv4l2src.c: (gst_v4l2src_init):
Use define here.
* sys/v4l2/gstv4l2tuner.c:
(gst_v4l2_tuner_set_frequency_and_notify):
Don't touch the property - its still disabled.
* sys/v4l2/v4l2src_calls.c: (gst_v4l2src_probe_caps_for_format),
(gst_v4l2src_grab_frame), (gst_v4l2src_get_size_limits):
* sys/v4l2/v4l2src_calls.h:
Improve fallback format negotionation. Fixes #451388