drm/i915: Fix wrong return value in intel_atomic_check()

In the case of calling check_digital_port_conflicts() failed, a
negative error code -EINVAL should be returned.

Fixes: bf5da83e4b ("drm/i915: Move check_digital_port_conflicts() earier")
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200802111535.5200-1-tianjia.zhang@linux.alibaba.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
(cherry picked from commit 66b51b801d)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/display/intel_display.c

@@ -14930,7 +14930,7 @@ static int intel_atomic_check(struct drm_device *dev,
 	if (any_ms && !check_digital_port_conflicts(state)) {
 		drm_dbg_kms(&dev_priv->drm,
 			    "rejecting conflicting digital port configuration\n");
-		ret = EINVAL;
+		ret = -EINVAL;
 		goto fail;
 	}