cifs: don't return error from standard_receive3 after marking response malformed

standard_receive3 will check the validity of the response from the
server (via checkSMB). It'll pass the result of that check to handle_mid
which will dequeue it and mark it with a status of
MID_RESPONSE_MALFORMED if checkSMB returned an error. At that point,
standard_receive3 will also return an error, which will make the
demultiplex thread skip doing the callback for the mid.

This is wrong -- if we were able to identify the request and the
response is marked malformed, then we want the demultiplex thread to do
the callback. Fix this by making standard_receive3 return 0 in this
situation.

Cc: stable@vger.kernel.org
Reported-and-Tested-by: Mark Moseley <moseleymark@gmail.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>