Make RS compile on ARM64.

bug 13280327

Change-Id: I79080c448ca17d0cba8df075737c22b24ce9a085
diff --git a/driver/rsdMeshObj.cpp b/driver/rsdMeshObj.cpp
index e8df21f..66c3b18 100644
--- a/driver/rsdMeshObj.cpp
+++ b/driver/rsdMeshObj.cpp
@@ -126,7 +126,7 @@
 }
 
 void RsdMeshObj::renderPrimitiveRange(const Context *rsc, uint32_t primIndex,
-                                      uint32_t start, uint32_t len) const {
+                                      size_t start, uint32_t len) const {
     if (len < 1 || primIndex >= mRSMesh->mHal.state.primitivesCount || mAttribCount == 0) {
         rsc->setError(RS_ERROR_FATAL_DRIVER, "Invalid mesh or parameters");
         return;