Fix all GCC 10 warnings

Change-Id: Ibabab265e734a4a421a38ab586e7e11905fa5da1
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/64740
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>
diff --git a/src/dawn_native/vulkan/UtilsVulkan.cpp b/src/dawn_native/vulkan/UtilsVulkan.cpp
index fd7a4ae..b04c0a4 100644
--- a/src/dawn_native/vulkan/UtilsVulkan.cpp
+++ b/src/dawn_native/vulkan/UtilsVulkan.cpp
@@ -44,8 +44,9 @@
                 return VK_COMPARE_OP_ALWAYS;
 
             case wgpu::CompareFunction::Undefined:
-                UNREACHABLE();
+                break;
         }
+        UNREACHABLE();
     }
 
     // Convert Dawn texture aspects to  Vulkan texture aspect flags