media: v4l2-dev.c: check for V4L2_CAP_STREAMING to enable streaming ioctls

Rather than checking which device type it is, just check the STREAMING
cap since that indicates support for streaming ioctls.

Some drivers only support READWRITE (typically MPEG encoders).

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>