CIFS: Fix handle_cancelled_mid callback initialization

Commit 99e214e0 ("Handle mismatched open calls") was applied with
errors that result in initializing handle_cancelled_mid callback twice
in smb21_operations and smb30_operations structures but not initializing
it in smb20_operations structure.

Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>