drm/i915/tv: Fix interlaced ysize calculation

Fix the calculation of the vertical active period for interlaced
TV modes.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181112170000.27531-4-ville.syrjala@linux.intel.comReviewed-by: Imre Deak <imre.deak@intel.com>

drivers/gpu/drm/i915/intel_tv.c

@@ -1086,7 +1086,7 @@ static void intel_tv_pre_enable(struct intel_encoder *encoder,
 	if (tv_mode->progressive)
 		ysize = tv_mode->nbr_end + 1;
 	else
-		ysize = 2*tv_mode->nbr_end + 1;
+		ysize = 2 * (tv_mode->nbr_end + 1);
 
 	xpos += conn_state->tv.margins.left;
 	ypos += conn_state->tv.margins.top;