tda19988: Fix divisor calculation

The existing calculation was linear with a fixup to make it non-linear
(and, correctly, cap it at 3). However, the actual value is logarithmic
and this ended up generating bad values in the following ranges:

* [20000, 37125] - gave a divisor of 3 not 2
* [40000, 49500] - gave a divisor of 2 not 1
* [74251, 79999] - gave a divisor of 0 not 1

Author: jrtc27

sys/dev/drm/bridges/tda19988/tda19988.c

@@ -778,12 +778,7 @@ tda19988_bridge_mode_set(struct drm_bridge *bridge,
 		vs2_line_end = vs2_line_start + (mode->vsync_end - mode->vsync_start)/2;
 	}
 
-	div = 148500 / mode->crtc_clock;
-	if (div != 0) {
-		div--;
-		if (div > 3)
-			div = 3;
-	}
+	div = imin(imax(fls(160000 / (mode->crtc_clock + 1)) - 1, 0), 3);
 
 	/* set HDMI HDCP mode off */
 	tda19988_reg_set(sc, TDA_TBG_CNTRL_1, TBG_CNTRL_1_DWIN_DIS);