Recent change brings potential leak of value on kernel stack to userspace
due to uninitialized value.

This commit fixes the bug.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: baa914cd ("firewire: add kernel API to access CYCLE_TIME register")
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20220512112037.103142-1-o-takashi@sakamocchi.jpSigned-off-by: Takashi Iwai <tiwai@suse.de>