ice: fix format issue

Change-Id: I0cfedfa1ef932585a108d3ea0c558e3277b59e81
diff --git a/src/ice_transport.cpp b/src/ice_transport.cpp
index 12c0122..1b8ef83 100644
--- a/src/ice_transport.cpp
+++ b/src/ice_transport.cpp
@@ -1317,7 +1317,7 @@
 {
     if (pimpl_->streamsCount_ != 1) {
         if (pimpl_->logger_)
-            pimpl_->logger_->error(FMT_STRING("Expected exactly one stream per SDP (found {:u} streams)"), pimpl_->streamsCount_);
+            pimpl_->logger_->error(FMT_STRING("Expected exactly one stream per SDP (found {:d} streams)"), pimpl_->streamsCount_);
         return false;
     }