ubifs: Check ubifs_wbuf_sync() return code

ubifs: Check ubifs_wbuf_sync() return code

[ Upstream commit aac17948a7ce01fb60b9ee6cf902967a47b3ce26 ]

If ubifs_wbuf_sync() fails we must not write a master node with the
dirty marker cleared.
Otherwise it is possible that in case of an IO error while syncing we
mark the filesystem as clean and UBIFS refuses to recover upon next
mount.

Cc: <stable@vger.kernel.org>
Fixes: 1e51764a3c2a ("UBIFS: add new flash file system")
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>