drm/i915: Correct the Ref clock value for BXT

The reference clock for BXT is 19.2 MHz not 19.5 MHz, updating the
correct value here.
Signed-off-by: Deepak M <m.deepak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1449238659-12473-2-git-send-email-m.deepak@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -7714,7 +7714,7 @@ enum skl_disp_power_wells {
 #define BXT_DSI_PLL_RATIO_MAX		0x7D
 #define BXT_DSI_PLL_RATIO_MIN		0x22
 #define BXT_DSI_PLL_RATIO_MASK		0xFF
-#define BXT_REF_CLOCK_KHZ		19500
+#define BXT_REF_CLOCK_KHZ		19200
 
 #define BXT_DSI_PLL_ENABLE		_MMIO(0x46080)
 #define  BXT_DSI_PLL_DO_ENABLE		(1 << 31)