No need to warn unregister_blkdev() failure by caller.  (The previous patch
makes unregister_blkdev() print error message in error case)
Acked-by: NGrant Likely <grant.likely@secretlab.ca>
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>