pcm: hw: do not reset tstamp_type in SND_PCM_APPEND mode

pcm: hw: do not reset tstamp_type in SND_PCM_APPEND mode

When the first client of plugins such as dshare open the hw device they set
a default tstamp_type in snd_pcm_direct_initialize_slave based on
tstamp_type from the config file. But when subsequent clients open the same
plugin the snd_pcm_hw_open_fd function clobbers this default.

Closes: https://github.com/alsa-project/alsa-lib/pull/450
Signed-off-by: Kevin Groeneveld <kgroeneveld@lenbrook.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>