libgsmhr/libgsmhr.c: fix memory leak after gsmhr_exit()

During the HR codec initialization, a part of the state is
allocated, but not freed at exit. Let's fix this.

Found during debugging with Valgrind:

4,932 bytes in 1 blocks are definitely lost in loss record 177 of 179
at 0x4C2AB80: malloc (in vgpreload_memcheck-amd64-linux.so)
by 0x6381C8F: gsmhr_init (libgsmhr.c:63)
by 0x526DF62: osmo_gapk_pq_queue_codec (pq_codec.c:48)
by 0x401ACE: make_processing_chain (app_osmo_gapk.c:573)
by 0x401ACE: main (app_osmo_gapk.c:765)

Change-Id: Ie9ead89c2272782de8d928f29753e6a523cf8834

libgsmhr/libgsmhr.c

@@ -79,6 +79,7 @@ gsmhr_init(void)
 EXPORT void
 gsmhr_exit(struct gsmhr *state)
 {
+	free(state->bss_save);
 	free(state);
 }