firewire: core: fix type of timestamp for async_inbound_template tracepoints events

The type of time stamp should be u16, instead of u8.

Link: https://lore.kernel.org/r/20240506082154.396077-1-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>