cifs: sanitize paths in cifs_update_super_prepath.

cifs: sanitize paths in cifs_update_super_prepath.

[ Upstream commit d19342c6609b67f2ba83b9eccca2777e3687f625 ]

After a server reboot, clients are failing to move files with ENOENT.
This is caused by DFS referrals containing multiple separators, which
the server move call doesn't recognize.

v1: Initial patch.
v2: Move prototype to header.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=2182472
Fixes: 726365ac8a5d ("cifs: sanitize multiple delimiters in prepath")
Actually-Fixes: 6c525ac49b92 ("cifs: switch to new mount api")
Reviewed-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Thiago Rafael Becker <tbecker@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>