drm/i915/dp: return proper DPRX link training result

commit 9af4bf2 upstream.

After DPRX link training, intel_dp_link_train_phy() did not
return the training result properly. If link training failed,
i915 driver would not run into link train fallback function.
And no hotplug uevent would be received by user space application.

Fixes: b30edfd ("drm/i915: Switch to LTTPR non-transparent mode link training")
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Cooper Chiou <cooper.chiou@intel.com>
Cc: William Tseng <william.tseng@intel.com>
Signed-off-by: Lee Shawn C <shawn.c.lee@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210706152541.25021-1-shawn.c.lee@intel.com
(cherry picked from commit dab1b47)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -848,7 +848,7 @@ intel_dp_link_train_all_phys(struct intel_dp *intel_dp,
 	}
 
 	if (ret)
-		intel_dp_link_train_phy(intel_dp, crtc_state, DP_PHY_DPRX);
+		ret = intel_dp_link_train_phy(intel_dp, crtc_state, DP_PHY_DPRX);
 
 	if (intel_dp->set_idle_link_train)
 		intel_dp->set_idle_link_train(intel_dp, crtc_state);