cifs: fail i/o on soft mounts if sessionsetup errors out

commit b0dd940e582b6a60296b9847a54012a4b080dc72 upstream.

RHBZ: 1579050

If we have a soft mount we should fail commands for session-setup
failures (such as the password having changed/ account being deleted/ ...)
and return an error back to the application.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>