snd_dlopen: do not use absolute plugin path for snd_dlopen() calls

snd_dlopen: do not use absolute plugin path for snd_dlopen() calls

In commit b906db19ef9f4fb7886003072e550391cc1ac651, the snd_dlopen()
implements the automatic lookup to the ALSA_PLUGIN_DIR directory.
It is not necessary to add the absolute paths in callers now.

The plugin names are also searched in ld.so.conf paths as the fallback now,
but it should not be a big problem.

BugLink: https://github.com/alsa-project/alsa-lib/issues/34
Signed-off-by: Jaroslav Kysela <perex@perex.cz>