cifs: fix memory leak of pneg_inbuf on -EOPNOTSUPP ioctl case

Currently in the case where SMB2_ioctl returns the -EOPNOTSUPP error
there is a memory leak of pneg_inbuf. Fix this by returning via
the out_free_inbuf exit path that will perform the relevant kfree.

Addresses-Coverity: ("Resource leak")
Fixes: 969ae8e8

 ("cifs: Accept validate negotiate if server return NT_STATUS_NOT_SUPPORTED")
CC: Stable <stable@vger.kernel.org> # v5.1+
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Steve French <stfrench@microsoft.com>