pcm: hw: Keep control data from kernel when SND_PCM_APPEND

Without this fix the application pointer would be reseted
whenever an application opens a device with SND_PCM_APPEND.

This would result in an Xrun if the device is already opened and
in running state and the appl_ptr is use.

Signed-off-by: Timo Wischer <twischer@de.adit-jv.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>