drm/amdgu: fix Unintentional integer overflow for mall size

Potentially overflowing expression mall_size_per_umc * adev->gmc.num_umc with type unsigned int (32 bits, unsigned)
is evaluated using 32-bit arithmetic,and then used in a context that expects an expression of type u64 (64 bits, unsigned).
Signed-off-by: Jesse Zhang <Jesse.Zhang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c

@@ -1629,7 +1629,7 @@ static int amdgpu_discovery_get_mall_info(struct amdgpu_device *adev)
 		break;
 	case 2:
 		mall_size_per_umc = le32_to_cpu(mall_info->v2.mall_size_per_umc);
-		adev->gmc.mall_size = mall_size_per_umc * adev->gmc.num_umc;
+		adev->gmc.mall_size = (uint64_t)mall_size_per_umc * adev->gmc.num_umc;
 		break;
 	default:
 		dev_err(adev->dev,