drm/amdkfd: Use resource_size() helper function

Use the resource_size() function instead of a open coded computation
resource size. It makes the code more readable.

Issue identified using resource_size.cocci coccinelle semantic patch.
Signed-off-by: Deepak R Varma <drv@mailo.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdkfd/kfd_migrate.c

@@ -1027,8 +1027,7 @@ int svm_migrate_init(struct amdgpu_device *adev)
 		/* Disable SVM support capability */
 		pgmap->type = 0;
 		if (pgmap->type == MEMORY_DEVICE_PRIVATE)
-			devm_release_mem_region(adev->dev, res->start,
-						res->end - res->start + 1);
+			devm_release_mem_region(adev->dev, res->start, resource_size(res));
 		return PTR_ERR(r);
 	}