drm/bridge: analogix_dp: Fix bailout for devm_drm_bridge_alloc()

devm_drm_bridge_alloc() returns ERR_PTR on failure instead of a
NULL pointer, so use IS_ERR() to check the returned pointer.
While at it, on failure, return ERR_CAST(dp) instead of
ERR_PTR(-ENOMEM) in order not to depend on devm_drm_bridge_alloc()
error code implementation.

Fixes: 48f05c3 ("drm/bridge: analogix_dp: Use devm_drm_bridge_alloc() API")
Signed-off-by: Liu Ying <victor.liu@nxp.com>
Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Link: https://lore.kernel.org/r/20250806095224.527938-1-victor.liu@nxp.com

Author: Liu Ying

drivers/gpu/drm/bridge/analogix/analogix_dp_core.c

@@ -1474,8 +1474,8 @@ analogix_dp_probe(struct device *dev, struct analogix_dp_plat_data *plat_data)
 
 	dp = devm_drm_bridge_alloc(dev, struct analogix_dp_device, bridge,
 				   &analogix_dp_bridge_funcs);
-	if (!dp)
-		return ERR_PTR(-ENOMEM);
+	if (IS_ERR(dp))
+		return ERR_CAST(dp);
 
 	dp->dev = &pdev->dev;
 	dp->dpms_mode = DRM_MODE_DPMS_OFF;