pcm: hw: add a helper function just to query status data

pcm: hw: add a helper function just to query status data

When mapping status data successfully, mapped page includes status data
for applications. In this case, applications have no need to call ioctl(2)
with SNDRV_PCM_IOCTL_SYNC_PTR. However, in current implementation, when
map of control data is unavailable, applications execute the ioctl(2).
This is inconvenient for some cases that applications require to query
status only.

This commit adds a helper function to query status data without issuing
the control in fallback mode from failure of status mmap.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>