drm/i915: Fix WARN_ON condition for cursor plane ddb allocation

In some cases like latency[level]==0, wm[level].res_lines>31,
min_ddb_alloc can be U16_MAX, exclude it from the WARN_ON.

v2: Specify the cases in which we hit U16_MAX, indentation (Ville)

Fixes: 10a7e07b ("drm/i915: Make sure cursor has enough ddb for the selected wm level")
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191216080619.10945-1-vandita.kulkarni@intel.com
(cherry picked from commit 4ba48701)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/intel_pm.c

@@ -4291,8 +4291,8 @@ skl_allocate_pipe_ddb(struct intel_crtc_state *crtc_state,
 				&crtc_state->wm.skl.optimal.planes[plane_id];
 
 			if (plane_id == PLANE_CURSOR) {
-				if (WARN_ON(wm->wm[level].min_ddb_alloc >
-					    total[PLANE_CURSOR])) {
+				if (wm->wm[level].min_ddb_alloc > total[PLANE_CURSOR]) {
+					WARN_ON(wm->wm[level].min_ddb_alloc != U16_MAX);
 					blocks = U32_MAX;
 					break;
 				}