ALSA: pcm: Fix structure definition for X32 ABI

X32 ABI uses the 64bit timespec in addition to 64bit alignment of 64bit
values. We have added compat ABI for these ioctls, but this patch adds
one missing padding into 'struct snd_pcm_mmap_status_x32' to fix
incompatibilities.

Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>