net: fix sock_timestamping_bind_phc() to release device

Don't forget to release the device in sock_timestamping_bind_phc() after
it was used to get the vclock indices.

Fixes: d463126e ("net: sock: extend SO_TIMESTAMPING for PHC binding")
Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
Cc: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>