drm/msm/dsi: do not try reading 28nm vco rate if it's not enabled

Reading VCO rate for this PLL can cause boot stalls, if it is not
enabled. Guard clk_hw_get_rate with a call to
dsi_pll_28nm_clk_is_enabled().
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/dsi/pll/dsi_pll_28nm.c

@@ -447,7 +447,10 @@ static void dsi_pll_28nm_save_state(struct msm_dsi_pll *pll)
 	cached_state->postdiv1 =
 			pll_read(base + REG_DSI_28nm_PHY_PLL_POSTDIV1_CFG);
 	cached_state->byte_mux = pll_read(base + REG_DSI_28nm_PHY_PLL_VREG_CFG);
-	cached_state->vco_rate = clk_hw_get_rate(&pll->clk_hw);
+	if (dsi_pll_28nm_clk_is_enabled(&pll->clk_hw))
+		cached_state->vco_rate = clk_hw_get_rate(&pll->clk_hw);
+	else
+		cached_state->vco_rate = 0;
 }
 
 static int dsi_pll_28nm_restore_state(struct msm_dsi_pll *pll)