pcm: hw: minor refactoring for initialization of control data

pcm: hw: minor refactoring for initialization of control data

At failure of control data mapping, alsa-lib goes to fallback mode. In
this mode, a buffer is kept in user space and executes ioctl(2) with
SNDRV_PCM_IOCTL_SYNC_PTR for the buffer to synchronize the control data.

In current implementation, no helper function is used for initialize
the control data. This commit use an proper helper function instead of
a direct call of ioctl(2).

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