Texture::GetTextureViewDescriptorWithDefaults: fix incorrect UNREACHABLE()

Bug: chromium:1230062

Change-Id: I3ff2638724d09079106ed048464d2640e206512e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/58500
Commit-Queue: Yunchao He <yunchao.he@intel.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>

src/dawn_native/Texture.cpp

@@ -390,7 +390,9 @@ namespace dawn_native {
                     desc.arrayLayerCount = texture->GetArrayLayers() - desc.baseArrayLayer;
                     break;
                 default:
-                    UNREACHABLE();
+                    // We don't put UNREACHABLE() here because we validate enums only after this
+                    // function sets default values. Otherwise, the UNREACHABLE() will be hit.
+                    break;
             }
         }
         if (desc.mipLevelCount == 0) {