dawn: Fix GCC warnings about functions not returning

Change-Id: Ia55a6549508a3259b97a35d2c06659a86633bc9e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/94321
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>

generator/templates/dawn/common/GPUInfo.cpp

@@ -101,6 +101,8 @@ std::string GetArchitectureName(PCIVendorID vendorId, PCIDeviceID deviceId) {
             {% endfor %}
         {% endfor %}
     }
+
+    return "";
 }
 
 }  // namespace gpu_info