Add the missing mutex_unlock before return from function
ocelot_hwstamp_set() in the ocelot_setup_ptp_traps() error
handling case.

Fixes: 96ca08c0 ("net: mscc: ocelot: set up traps for PTP packets")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20211129151652.1165433-1-weiyongjun1@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>