gst/gstbuffer.c: Small docs update.

gst/gstbuffer.c: Small docs update.

Original commit message from CVS:
* gst/gstbuffer.c:
Small docs update.

* gst/gstcaps.c: (gst_caps_is_equal):
Don't assert on NULL <--> X. Fixes #323260

* gst/gstminiobject.c: (gst_mini_object_replace):
If we're doing atomic operations, we might just as well use
the proper way to get an atomic pointer.

* libs/gst/base/gstbasesink.c: (gst_base_sink_get_position):
Clean up debugging.