Bluetooth: SMP: make SM/PER/KDU/BI-04-C happy

The last test step ("Test with Invalid public key X and Y, all set to
0") expects to get an "DHKEY check failed" instead of "unspecified".

Fixes: 6d19628f539f ("Bluetooth: SMP: Fail if remote and local public keys are identical")
Signed-off-by: Christian Eggers <ceggers@arri.de>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>