CIFS: Fix NULL pointer deref on SMB2_tcon() failure

CIFS: Fix NULL pointer deref on SMB2_tcon() failure

BugLink: http://bugs.launchpad.net/bugs/1731961
commit db3b5474f462e77b82ca1e27627f03c47b622c99 upstream.

If SendReceive2() fails rsp is set to NULL but is dereferenced in the
error handling code.

Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <smfrench@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>