Btrfs: fix release reserved extents trace points

We were doing trace_btrfs_release_reserved_extent() in pin_down_extent which
isn't quite right because we will go through and free that extent later when we
unpin, so it messes up apps that are accounting for the reservation space.  We
were also unconditionally doing it in __btrfs_free_reserved_extent(), when we
only actually free the reservation instead of pinning the extent.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>