drm/radeon: prefer lower reference dividers

Instead of the closest reference divider prefer the lowest,
this fixes flickering issues on HP Compaq nx9420.

Bugs: https://bugs.freedesktop.org/show_bug.cgi?id=108514
Suggested-by: Paul Dufresne <dufresnep@gmail.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

drivers/gpu/drm/radeon/radeon_display.c

@@ -922,12 +922,12 @@ static void avivo_get_fb_ref_div(unsigned nom, unsigned den, unsigned post_div,
 	ref_div_max = max(min(100 / post_div, ref_div_max), 1u);
 
 	/* get matching reference and feedback divider */
-	*ref_div = min(max(DIV_ROUND_CLOSEST(den, post_div), 1u), ref_div_max);
+	*ref_div = min(max(den/post_div, 1u), ref_div_max);
 	*fb_div = DIV_ROUND_CLOSEST(nom * *ref_div * post_div, den);
 
 	/* limit fb divider to its maximum */
 	if (*fb_div > fb_div_max) {
-		*ref_div = DIV_ROUND_CLOSEST(*ref_div * fb_div_max, *fb_div);
+		*ref_div = (*ref_div * fb_div_max)/(*fb_div);
 		*fb_div = fb_div_max;
 	}
 }