drm/i915: Use fixed_16_16 wrapper for division operation

Don't use fixed_16_16 structure members directly, instead use wrapper to
perform fixed_16_16 division operation.

Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170517115831.13830-4-mahesh1.kumar@intel.com

drivers/gpu/drm/i915/intel_pm.c

@@ -4334,8 +4334,8 @@ static int skl_compute_plane_wm(const struct drm_i915_private *dev_priv,
 	}
 
 	res_blocks = fixed_16_16_to_u32_round_up(selected_result) + 1;
-	res_lines = DIV_ROUND_UP(selected_result.val,
-				 plane_blocks_per_line.val);
+	res_lines = div_round_up_fixed16(selected_result,
+					 plane_blocks_per_line);
 
 	if (level >= 1 && level <= 7) {
 		if (y_tiled) {