sysfile: Make sys_readdir take a const prevptr
sysfile: Make sys_readdir take a const prevptr

bowlofstew/sv6,aclements/sv6,aclements/sv6,bowlofstew/sv6,bowlofstew/sv6,aclements/sv6,bowlofstew/sv6,aclements/sv6,aclements/sv6,bowlofstew/sv6