ptp: ptp_clockmatrix: Fix missing unlock on error in idtcm_probe()

Add the missing unlock before return from function idtcm_probe()
in the error handling case.

Fixes: 3a6ba7dc ("ptp: Add a ptp clock driver for IDT ClockMatrix.")
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: NVincent Cheng <vincent.cheng.xh@renesas.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/ptp/ptp_clockmatrix.c

@@ -1294,8 +1294,10 @@ static int idtcm_probe(struct i2c_client *client,
 
 	err = set_tod_write_overhead(idtcm);
 
-	if (err)
+	if (err) {
+		mutex_unlock(&idtcm->reg_lock);
 		return err;
+	}
 
 	err = idtcm_load_firmware(idtcm, &client->dev);