btrfs: fix incorrect log message for nobarrier mount option

Fix a wrong log message that appears when the "nobarrier" mount option
is unset.  When "nobarrier" is unset, barrier is actually enabled.
However, the log incorrectly stated "turning off barriers".

Fixes: eddb1a43 ("btrfs: add reconfigure callback for fs_context")
CC: stable@vger.kernel.org # 6.12+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Kyoji Ogasawara <sawara04.o@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>