[ALSA] Fix probe of non-PnP ISA devices

isa_register_driver() returns an error if no device is found
and it's no fatal error for the drivers with pnp support.

Signed-off-by: Rene Herman <rene.herman@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>