pcm: fix 64-bit SNDRV_PCM_IOCTL_STATUS ABI breakage

pcm: fix 64-bit SNDRV_PCM_IOCTL_STATUS ABI breakage

Commit cf40ea169aad (pcm: support for audio timestamps) added the new
audio_tstamp field to struct sndrv_pcm_status.  However, struct timespec
requires 64-bit alignment, so the 64-bit compiler would insert
32 bits of padding before this field, which broke SNDRV_PCM_IOCTL_STATUS
with error messages like this:

      kernel: unknown ioctl = 0x80984120

To solve this, insert the padding explicitly so that it can be taken
into account when calculating the ABI structure size.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>