Fix: add missing buffer registry cleanup on error

Fixes #542

Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: remove one too many metadata refcount increment

The refcount increment is removed from the add metadata stream function
so for both kernel and UST, the increment is done once the stream is
allocated and the channel reference is set.

Signed-off-by: David Goulet <dgoulet@efficios.com>