smb3: fix Open files on server counter going negative

We were decrementing the count of open files on server twice
for the case where we were closing cached directories.

Fixes: 8e843bf3 ("cifs: return a single-use cfid if we did not get a lease")
Cc: stable@vger.kernel.org
Acked-by: Bharath SM <bharathsm@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>