marl: Fix compiler warning treated as error.

Will be upstreamed.

Bug: b/140546382
Change-Id: Ifbbc14d5c5cd1cb6940642a1e6cc690c224e9bfe
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/36068
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>

third_party/marl/src/scheduler.cpp

diff --git a/third_party/marl/src/scheduler.cpp b/third_party/marl/src/scheduler.cpp
index 0ccd569..ca21cdd 100644
--- a/third_party/marl/src/scheduler.cpp
+++ b/third_party/marl/src/scheduler.cpp
@@ -476,7 +476,7 @@
 }
 
 Scheduler::Fiber* Scheduler::Worker::createWorkerFiber() {
-  auto id = workerFibers.size() + 1;
+  auto id = static_cast<uint32_t>(workerFibers.size() + 1);
   auto fiber = Fiber::create(id, FiberStackSize, [&] { run(); });
   workerFibers.push_back(std::unique_ptr<Fiber>(fiber));
   return fiber;