ALSA: timer: Fix leak in SNDRV_TIMER_IOCTL_PARAMS

The stack object “tread” has a total size of 32 bytes. Its field
“event” and “val” both contain 4 bytes padding. These 8 bytes
padding bytes are sent to user without being initialized.

Change-Id: Ibf2868136a538eed0f2e75395a5f14a8608dd86d
Signed-off-by: Kangjie Lu <kjlu@gatech.edu>
Signed-off-by: Takashi Iwai <tiwai@suse.de>