dtlk: fix error checks in module_init()

This patch fixes two things in module_init.

- fix register_chrdev() error check

  Currently dtlk doesn't check register_chrdev() failure correctly.
  register_chrdev() returns a errno on failure.

- check probe failure

  dtlk ignores probe failure and allows the module loading without
  such device. I got "Trying to free nonexistent resource" message
  by release_region() when unloading module without device.

[akpm@linux-foundation.org: fix error code return]
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Chris Pallotta <chris@allmedia.com>
Cc: Jim Van Zandt <jrv@vanzandt.mv.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>