Cast the scratch resource key in order to fix a warning

src/gpu/GrResourceCache2.cpp

Index: src/gpu/GrResourceCache2.cpp
diff --git a/src/gpu/GrResourceCache2.cpp b/src/gpu/GrResourceCache2.cpp
index ccfe382733fa94383c09bd48da8cef75bfe5a86b..0a6705a5c4dd13b4bce1a7779c0ab1e6f649483b 100644
--- a/src/gpu/GrResourceCache2.cpp
+++ b/src/gpu/GrResourceCache2.cpp
@@ -21,12 +21,12 @@ DECLARE_SKMESSAGEBUS_MESSAGE(GrResourceInvalidatedMessage);
 GrScratchKey::ResourceType GrScratchKey::GenerateResourceType() {
     static int32_t gType = kInvalidResourceType + 1;
 
-    int32_t type = sk_atomic_inc(&gType);
+    ResourceType type = static_cast<ResourceType>(sk_atomic_inc(&gType));
     if (kInvalidResourceType == type) {
         SkFAIL("Too many Resource Types");
     }
 
-    return static_cast<ResourceType>(type);
+    return type;
 }