Zero-initialize SDL_GPUDevice

(cherry picked from commit 86da08b0be)

src/gpu/vulkan/SDL_gpu_vulkan.c

@@ -11779,7 +11779,7 @@ static SDL_GPUDevice *VULKAN_CreateDevice(bool debugMode, bool preferLowPower, S
     }
 
     // FIXME: just move this into this function
-    result = (SDL_GPUDevice *)SDL_malloc(sizeof(SDL_GPUDevice));
+    result = (SDL_GPUDevice *)SDL_calloc(1, sizeof(SDL_GPUDevice));
     ASSIGN_DRIVER(VULKAN)
 
     result->driverData = (SDL_GPURenderer *)renderer;