[media] v4l: Copy timestamp source flags to destination on m2m devices

Copy the flags containing the timestamp source from source buffer flags to
the destination buffer flags on memory-to-memory devices. This is analogous
to copying the timestamp field from source to destination.

Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Acked-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>