drm/amd/display: Add NULL pointer checks in dm_force_atomic_commit()

This commit updates the dm_force_atomic_commit function to replace the
usage of PTR_ERR_OR_ZERO with IS_ERR for checking error states after
retrieving the Connector (drm_atomic_get_connector_state), CRTC
(drm_atomic_get_crtc_state), and Plane (drm_atomic_get_plane_state)
states.

The function utilized PTR_ERR_OR_ZERO for error checking. However, this
approach is inappropriate in this context because the respective
functions do not return NULL; they return pointers that encode errors.

This change ensures that error pointers are properly checked using
IS_ERR before attempting to dereference.

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Cc: Tom Chung <chiahsuan.chung@amd.com>
Cc: Roman Li <roman.li@amd.com>
Cc: Alex Hung <alex.hung@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@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

@@ -10602,26 +10602,32 @@ static int dm_force_atomic_commit(struct drm_connector *connector)
 	 */
 	conn_state = drm_atomic_get_connector_state(state, connector);
 
-	ret = PTR_ERR_OR_ZERO(conn_state);
-	if (ret)
+	/* Check for error in getting connector state */
+	if (IS_ERR(conn_state)) {
+		ret = PTR_ERR(conn_state);
 		goto out;
+	}
 
 	/* Attach crtc to drm_atomic_state*/
 	crtc_state = drm_atomic_get_crtc_state(state, &disconnected_acrtc->base);
 
-	ret = PTR_ERR_OR_ZERO(crtc_state);
-	if (ret)
+	/* Check for error in getting crtc state */
+	if (IS_ERR(crtc_state)) {
+		ret = PTR_ERR(crtc_state);
 		goto out;
+	}
 
 	/* force a restore */
 	crtc_state->mode_changed = true;
 
 	/* Attach plane to drm_atomic_state */
 	plane_state = drm_atomic_get_plane_state(state, plane);
 
-	ret = PTR_ERR_OR_ZERO(plane_state);
-	if (ret)
+	/* Check for error in getting plane state */
+	if (IS_ERR(plane_state)) {
+		ret = PTR_ERR(plane_state);
 		goto out;
+	}
 
 	/* Call commit internally with the state we just constructed */
 	ret = drm_atomic_commit(state);