drm/radeon/kms: switch back to min->max pll post divider iteration

Seems more reliable.  Fixes:
https://bugzilla.kernel.org/show_bug.cgi?id=26552

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_display.c

@@ -849,7 +849,7 @@ void radeon_compute_pll(struct radeon_pll *pll,
 		max_fractional_feed_div = pll->max_frac_feedback_div;
 	}
 
-	for (post_div = max_post_div; post_div >= min_post_div; --post_div) {
+	for (post_div = min_post_div; post_div <= max_post_div; ++post_div) {
 		uint32_t ref_div;
 
 		if ((pll->flags & RADEON_PLL_NO_ODD_POST_DIV) && (post_div & 1))