Bluetooth: Add debug statement

Change-Id: I8308c31dc0916b8f2e7858f48e7fd2346164f333
Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>

net/bluetooth/smp.c

@@ -1237,6 +1237,7 @@ static int bt_smp_aes_cmac(const uint8_t *key, const uint8_t *in, size_t len,
 	/* (K1,K2) = Generate_Subkey(K) */
 	err = cmac_subkey(key_s, k1, k2);
 	if (err) {
+		BT_ERR("SMAC subkey generation failed\n");
 		return err;
 	}