[media] s5p-mfc: Make 'clk_ref' static in s5p_mfc_pm.c

Fixes the following sparse warning:
drivers/media/platform/s5p-mfc/s5p_mfc_pm.c:31:10: warning:
symbol 'clk_ref' was not declared. Should it be static?
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/platform/s5p-mfc/s5p_mfc_pm.c

@@ -28,7 +28,7 @@ static struct s5p_mfc_pm *pm;
 static struct s5p_mfc_dev *p_dev;
 
 #ifdef CLK_DEBUG
-atomic_t clk_ref;
+static atomic_t clk_ref;
 #endif
 
 int s5p_mfc_init_pm(struct s5p_mfc_dev *dev)