Add snd_lib_error_set_local() to install a thread-local error handler.

Add snd_lib_error_set_local() to install a thread-local error handler.

This is required so we can make other functions reentrant (such as
snd_device_name_hint()).
The default error handling function snd_lib_error_default() now checks
if a local handler exists, and if so, calls it. Otherwise, the previous
behavior is unchanged.

Signed-off-by: Jerome Forissier <jerome@taodyne.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>