cuda : skip UMA override for HIP builds (#27083)

AMD APUs report accurate memory via hipMemGetInfo. Using
MemAvailable over-promises on small-carveout systems.

fixes #18159

ggml/src/ggml-cuda/ggml-cuda.cu

@@ -4770,7 +4770,7 @@ static void ggml_backend_cuda_device_get_memory(ggml_backend_dev_t dev, size_t *
     }
 
 // ref: https://github.com/ggml-org/llama.cpp/pull/17368
-#if defined(__linux__)
+#if defined(__linux__) && !defined(GGML_USE_HIP)
     // Check if this is a UMA (Unified Memory Architecture) system
     cudaDeviceProp prop;
     CUDA_CHECK(cudaGetDeviceProperties(&prop, ggml_cuda_get_physical_device(ctx->device)));
@@ -4790,7 +4790,7 @@ static void ggml_backend_cuda_device_get_memory(ggml_backend_dev_t dev, size_t *
             GGML_LOG_ERROR("%s: /proc/meminfo reading failed, using cudaMemGetInfo\n", __func__);
         }
     }
-#endif // defined(__linux__)
+#endif // defined(__linux__) && !defined(GGML_USE_HIP)
 
     // virtual devices sharing one physical GPU share its memory pool; split it between them
     const int share_count = ggml_cuda_physical_device_share_count(ctx->device);