drm: of: Fix linking when CONFIG_OF is not set

The new helper drm_of_lvds_get_dual_link_pixel_order() introduced in
commit 65290075 has a fallback stub when CONFIG_OF is not set, but
the stub is declared in drm_of.h without a static inline. This causes
multiple definitions of the function to be linked when the CONFIG_OF
option isn't set. Fix it by making the stub static inline.

Fixes: 65290075 ("drm: of: Add drm_of_lvds_get_dual_link_pixel_order")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191219103703.8547-1-laurent.pinchart+renesas@ideasonboard.com

include/drm/drm_of.h

@@ -92,7 +92,8 @@ static inline int drm_of_find_panel_or_bridge(const struct device_node *np,
 	return -EINVAL;
 }
 
-int drm_of_lvds_get_dual_link_pixel_order(const struct device_node *port1,
+static inline int
+drm_of_lvds_get_dual_link_pixel_order(const struct device_node *port1,
 				      const struct device_node *port2)
 {
 	return -EINVAL;