xfs: fix remount rw with unrecognized options

When we skip unrecognized options in xfs_fs_remount we should just break
out of the switch and not return because otherwise we may skip clearing
the xfs-internal read-only flag.  This will only show up on some
operations like touch because most read-only checks are done by the VFS
which thinks this filesystem is r/w.  Eventually we should replace the
XFS read-only flag with a helper that always checks the VFS flag to make
sure they can never get out of sync.

Bug reported and fix verified by Marcel Beister on #xfs.
Bug fix verified by updated xfstests/189.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: Timothy Shimmin <tes@sgi.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>