Rename buffer status to make it more symetrical

Only try to pull once in a timeout.
We can reuse the last returned state as our internal state in
audiomixer.

spa/include/spa/defs.h

@@ -41,8 +41,8 @@ typedef enum {
   SPA_RESULT_NO_FORMAT                 = -4,
   SPA_RESULT_INVALID_COMMAND           = -5,
   SPA_RESULT_INVALID_PORT              = -6,
-  SPA_RESULT_HAVE_OUTPUT               = -7,
-  SPA_RESULT_NEED_INPUT                = -8,
+  SPA_RESULT_HAVE_BUFFER               = -7,
+  SPA_RESULT_NEED_BUFFER               = -8,
   SPA_RESULT_PORTS_CHANGED             = -9,
   SPA_RESULT_FORMAT_CHANGED            = -10,
   SPA_RESULT_PROPERTIES_CHANGED        = -11,