drm/amd/display: Add NULL check for stream before dereference in 'dm_vupdate_high_irq'

Add a NULL check for acrtc->dm_irq_params.stream before
accessing its members.

Fixes below:
drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:623
dm_vupdate_high_irq() warn: variable dereferenced before check
'acrtc->dm_irq_params.stream' (see line 615)

614	if (vrr_active) {
615		bool replay_en = acrtc->dm_irq_params.stream->link->replay_settings.replay_feature_enabled;
				 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
616		bool psr_en = acrtc->dm_irq_params.stream->link->psr_settings.psr_feature_enabled;
			      ^^^^^^^^^^^^^^^^^^^^^^^^^^^ New dereferences

617		bool fs_active_var_en = acrtc->dm_irq_params.freesync_config.state
618			== VRR_STATE_ACTIVE_VARIABLE;
619
620		amdgpu_dm_crtc_handle_vblank(acrtc);
621
622		/* BTR processing for pre-DCE12 ASICs */
623		if (acrtc->dm_irq_params.stream &&
		    ^^^^^^^^^^^^^^^^^^^^^^^^^^^ But the existing code assumed it could be NULL. Someone is wrong.

624		    adev->family < AMDGPU_FAMILY_AI) {
625			spin_lock_irqsave(&adev_to_drm(adev)->event_lock, flags);

Fixes: 6d31602 ("drm/amd/display: more liberal vmin/vmax update for freesync")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Cc: Alex Hung <alex.hung@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Cc: Roman Li <roman.li@amd.com>
Cc: ChiaHsuan Chung <chiahsuan.chung@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Ray Wu <ray.wu@amd.com>
Cc: Daniel Wheeler <daniel.wheeler@amd.com>
Cc: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: srishanm

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -611,7 +611,7 @@ static void dm_vupdate_high_irq(void *interrupt_params)
 		 * page-flip completion events that have been queued to us
 		 * if a pageflip happened inside front-porch.
 		 */
-		if (vrr_active) {
+		if (vrr_active && acrtc->dm_irq_params.stream) {
 			bool replay_en = acrtc->dm_irq_params.stream->link->replay_settings.replay_feature_enabled;
 			bool psr_en = acrtc->dm_irq_params.stream->link->psr_settings.psr_feature_enabled;
 			bool fs_active_var_en = acrtc->dm_irq_params.freesync_config.state
@@ -620,8 +620,7 @@ static void dm_vupdate_high_irq(void *interrupt_params)
 			amdgpu_dm_crtc_handle_vblank(acrtc);
 
 			/* BTR processing for pre-DCE12 ASICs */
-			if (acrtc->dm_irq_params.stream &&
-			    adev->family < AMDGPU_FAMILY_AI) {
+			if (adev->family < AMDGPU_FAMILY_AI) {
 				spin_lock_irqsave(&adev_to_drm(adev)->event_lock, flags);
 				mod_freesync_handle_v_update(
 				    adev->dm.freesync_module,