Fix illegal cast in a logging code

This is a follow up CL for I19ad8542659bc092b92ee13eb9,
which introduced a ClassCastException error in the logging code
of MSG_SET_USER_ACTION_NOTIFICATION_SEQUENCE_NUMBER handler.

With this CL, the protocol in question looks like:
- what: MSG_SET_USER_ACTION_NOTIFICATION_SEQUENCE_NUMBER
- arg1: sequence number to be passed to
    #setUserActionNotificationSequenceNumber(int)
- arg2: not used
- obj:  ClientState

BUG: 16238154
BUG: 7043015
Change-Id: I08d52d4564bae9e042a2eff359e92549a66e837b