D3D8: Make some test functions static

[H. Verbeet]

Changelog:
  -  Make some test functions static
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diff --git a/dlls/d3d8/tests/device.c b/dlls/d3d8/tests/device.c
index 5a5ac79..89986f8 100644
--- a/dlls/d3d8/tests/device.c
+++ b/dlls/d3d8/tests/device.c
@@ -37,7 +37,7 @@ static int get_refcount(IUnknown *object
         trace("%s failed: %s\n", c, DXGetErrorString8(r)); \
     }
 
-void test_swapchain(void)
+static void test_swapchain(void)
 {
     HRESULT                      hr;
     HWND                         hwnd               = NULL;
@@ -153,7 +153,7 @@ void test_swapchain(void)
     DestroyWindow( hwnd );
 }
 
-void test_refcount(void)
+static void test_refcount(void)
 {
     HRESULT                      hr;
     HWND                         hwnd               = NULL;