Dont allocate a new image which already has mip levels, when regenerating vulkan mipmaps

src/gpu/vk/GrVkImage.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrVkImage_DEFINED
 #define GrVkImage_DEFINED
 
@@ skipping 25 matching lines @@
             fResource = new BorrowedResource(info.fImage, info.fAlloc, info.fImageTiling);
         } else {
             fResource = new Resource(info.fImage, info.fAlloc, info.fImageTiling);
         }
     }
     virtual ~GrVkImage();
 
     VkImage image() const { return fInfo.fImage; }
     const GrVkAlloc& alloc() const { return fInfo.fAlloc; }
     VkFormat imageFormat() const { return fInfo.fFormat; }
+    uint32_t mipLevels() const { return fInfo.fLevelCount; }
     const Resource* resource() const { return fResource; }
     bool isLinearTiled() const {
         return SkToBool(VK_IMAGE_TILING_LINEAR == fInfo.fImageTiling);
     }
 
     VkImageLayout currentLayout() const { return fInfo.fImageLayout; }
 
     void setImageLayout(const GrVkGpu* gpu,
                         VkImageLayout newLayout,
                         VkAccessFlags dstAccessMask,
@@ skipping 75 matching lines @@
     private:
         void freeGPUData(const GrVkGpu* gpu) const override;
     };
 
     const Resource* fResource;
 
     friend class GrVkRenderTarget;
 };
 
 #endif