cifs: fix a possible use of uninit variable in SMB2_sess_setup

In case of error, goto ssetup_exit can be hit and we could end up using
uninitialized value of resp_buftype

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
Signed-off-by: Steve French <smfrench@gmail.com>