Missing NULL check on vfsconf_find_by_name("devfs") before dereference in vfs_mountroot_devfs

Summary

vfs_mountroot_devfs (vfs_conf.c:300-311): vfsp=vfsconf_find_by_name("devfs") immediately dereffed :306 mount_init(mp,vfsp->vfc_vfsops) :308 mp->mnt_vfc=vfsp :310 vfsp->vfc_refcount++ no NULL test. If devfs not registered -> NULL deref panic. Stock kernel always compiles devfs so never NULL in practice. Hardening gap no attacker trigger. Fix: if(vfsp==NULL) return ENODEV.