alsa: Fix compile warnings

modules/alsa/alsa-sink.c: In function ‘pa_alsa_sink_new’:
modules/alsa/alsa-sink.c:2603:15: warning: declaration of ‘state’ shadows a previous local [-Wshadow]
         void *state;
               ^~~~~
modules/alsa/alsa-sink.c:2270:11: note: shadowed declaration is here
     void *state = NULL;
           ^~~~~
  CC       modules/alsa/module_alsa_sink_la-module-alsa-sink.lo
modules/alsa/alsa-source.c: In function ‘pa_alsa_source_new’:
modules/alsa/alsa-source.c:2289:15: warning: declaration of ‘state’ shadows a previous local [-Wshadow]
         void *state;
               ^~~~~
modules/alsa/alsa-source.c:1975:11: note: shadowed declaration is here
     void *state = NULL;
           ^~~~~
modules/alsa/module-alsa-card.c: In function ‘prune_singleton_availability_groups’:
modules/alsa/module-alsa-card.c:691:71: warning: pointer of type ‘void *’ used in arithmetic [-Wpointer-arith]
             pa_hashmap_put(group_counts, p->availability_group, count + 1);
                                                                       ^