omapfb: dss: Fix max fclk divider for omap36xx

The drm/omap driver was fixed to correct an issue where using a
divider of 32 breaks the DSS despite the TRM stating 32 is a valid
number.  Through experimentation, it appears that 31 works, and
it is consistent with the value used by the drm/omap driver.

This patch fixes the divider for fbdev driver instead of the drm.

Fixes: f76ee89 ("omapfb: copy omapdss & displays for omapfb")
Cc: <[email protected]> #4.5+
Signed-off-by: Adam Ford <[email protected]>
Reviewed-by: Tomi Valkeinen <[email protected]>
Cc: Dave Airlie <[email protected]>
Cc: Rob Clark <[email protected]>
[b.zolnierkie: mark patch as applicable to stable 4.5+ (was 4.9+)]
Signed-off-by: Bartlomiej Zolnierkiewicz <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

drivers/video/fbdev/omap2/omapfb/dss/dss.c

@@ -836,7 +836,7 @@ static const struct dss_features omap34xx_dss_feats = {
 };
 
 static const struct dss_features omap3630_dss_feats = {
-	.fck_div_max		=	32,
+	.fck_div_max		=	31,
 	.dss_fck_multiplier	=	1,
 	.parent_clk_name	=	"dpll4_ck",
 	.dpi_select_source	=	&dss_dpi_select_source_omap2_omap3,