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

src/gpu/vk/GrVkImage.h

Index: src/gpu/vk/GrVkImage.h
diff --git a/src/gpu/vk/GrVkImage.h b/src/gpu/vk/GrVkImage.h
index 2bfc08d150ffa41fb179aa8111b415cac8d2a1c9..921d98e6acf9d3ee981d0fe9acf539e17c3e7b8e 100644
--- a/src/gpu/vk/GrVkImage.h
+++ b/src/gpu/vk/GrVkImage.h
@@ -43,6 +43,7 @@ public:
     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);