Another attempt to silence the warble build warning on 32-bit hosts

Change-Id: Ib83ce41582b18641badb389c3871e501c8be697f
diff --git a/lib/rbcodec/codecs/librm/rm.c b/lib/rbcodec/codecs/librm/rm.c
index 87474e4..318a9d0 100644
--- a/lib/rbcodec/codecs/librm/rm.c
+++ b/lib/rbcodec/codecs/librm/rm.c
@@ -604,6 +604,6 @@
     DEBUGF("block_align = %u\n", rmctx->block_align);
     DEBUGF("nb_channels = %u\n", rmctx->nb_channels);
     DEBUGF("sample_rate = %u\n", rmctx->sample_rate);
-    DEBUGF("bit_rate    = %lu\n", rmctx->bit_rate   );
+    DEBUGF("bit_rate    = %zu\n", rmctx->bit_rate   );
 }
 #endif