tempfile: update comments around bees_sync

Deadlock reproduced on kernel 4.14.34.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

src/bees.cc

@@ -614,6 +614,8 @@ BeesTempFile::make_copy(const BeesFileRange &src)
 #if 1
 		// Is this fixed by "Btrfs: fix deadlock between dedup on same file and starting writeback"?
 		// No.
+		// Is this fixed in kernel 4.14.34?
+		// No.
 		bees_sync(m_fd);
 #endif
 	}