drm/i915: Check SAGV wm min_ddb_alloc rather than plane_res_b

For non-transition watermarks we are supposed to check min_ddb_alloc
rather than plane_res_b when determining if we have enough DDB space
for it. A bit too much copy pasta made me check the wrong thing.

Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Fixes: df4a50a3 ("drm/i915: Zero out SAGV wm when we don't have enough DDB for it")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210305153610.12177-4-ville.syrjala@linux.intel.comReviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>

drivers/gpu/drm/i915/intel_pm.c

@@ -4989,7 +4989,7 @@ skl_allocate_plane_ddb(struct intel_atomic_state *state,
 		if (wm->trans_wm.plane_res_b >= total[plane_id])
 			memset(&wm->trans_wm, 0, sizeof(wm->trans_wm));
 
-		if (wm->sagv.wm0.plane_res_b >= total[plane_id])
+		if (wm->sagv.wm0.min_ddb_alloc > total[plane_id])
 			memset(&wm->sagv.wm0, 0, sizeof(wm->sagv.wm0));
 
 		if (wm->sagv.trans_wm.plane_res_b >= total[plane_id])