added const specifier in function, pcm_is_ready
diff --git a/src/pcm.c b/src/pcm.c
index 29c69a7..c32e8ab 100644
--- a/src/pcm.c
+++ b/src/pcm.c
@@ -979,7 +979,7 @@
  *  Otherwise, the function returns one.
  * @ingroup libtinyalsa-pcm
  */
-int pcm_is_ready(struct pcm *pcm)
+int pcm_is_ready(const struct pcm *pcm)
 {
     return pcm->fd >= 0;
 }