No need to warn unregister_blkdev() failure by the callers.  (The previous
patch makes unregister_blkdev() print error message in error case)
Signed-off-by: NAkinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>