Fixes blk_queue_resize_tags to properly handle allocation failures.

Currently, if a memory allocation failure occurs during
blk_queue_resize_tags, the tag map ends up getting freed, which should
not happen.  The old tag map should be preserved and only the resize
should fail.
Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Brian King <brking@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>