From:  Chris Wilson <chris@qwirx.com>

  This function did check misc_register's return code, but made no effort to
  clean up if it failed, leaving a large amount of potential crud lying
  around. I moved the registration to the start of the function, so that the
  cleanup is trivial, and made sure the device gets unregistered in the
  cases where it would not have been registered at all before.