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: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Vincent Cheng <vincent.cheng.xh@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>