Fix error on jack compilation with salsa

Fix error on jack compilation with salsa:
 /usr/include/alsa/ctl_macros.h:251:48: error: invalid conversion from
 'void*' to 'snd_ctl_elem_id_t* {aka snd_ctl_elem_id*}' [-fpermissive]

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/src/ctl_macros.h b/src/ctl_macros.h
index 2bfd3a4..9ed3357 100644
--- a/src/ctl_macros.h
+++ b/src/ctl_macros.h
@@ -248,7 +248,7 @@
 				  unsigned int entries)
 {
 	free(obj->pids);
-	obj->pids = calloc(entries, sizeof(*obj->pids));
+	obj->pids = (snd_ctl_elem_id_t*)calloc(entries, sizeof(*obj->pids));
 	if (!obj->pids) {
 		obj->space = 0;
 		return -ENOMEM;