net: marvell: prestera: fix NULL dereference on devlink_alloc() failure

[ Upstream commit a428e0d ]

devlink_alloc() may return NULL on allocation failure, but
prestera_devlink_alloc() unconditionally calls devlink_priv() on
the returned pointer.

This leads to a NULL pointer dereference if devlink allocation fails.
Add a check for a NULL devlink pointer and return NULL early to avoid
the crash.

Fixes: 34dd171 ("net: marvell: prestera: Add basic devlink support")
Signed-off-by: Alok Tiwari <alok.a.tiwari@oracle.com>
Acked-by: Elad Nachman <enachman@marvell.com>
Link: https://patch.msgid.link/20251230052124.897012-1-alok.a.tiwari@oracle.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: aloktiwa

drivers/net/ethernet/marvell/prestera/prestera_devlink.c

@@ -387,6 +387,8 @@ struct prestera_switch *prestera_devlink_alloc(struct prestera_device *dev)
 
 	dl = devlink_alloc(&prestera_dl_ops, sizeof(struct prestera_switch),
 			   dev->dev);
+	if (!dl)
+		return NULL;
 
 	return devlink_priv(dl);
 }