[media] videodev2.h: fix incorrect V4L2_DV_FL_HALF_LINE bitmask

This was set to 1 << 0 which is the same as V4L2_DV_FL_REDUCED_BLANKING.
It should be 1 << 3 instead. Luckily interlaced formats are rarely used,
which is why this bug wasn't seen until now.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>