block: drop duplicated slice extension code The current slice is extended when an I/O request exceeds the limit. There is no need to extend the slice every time we check a request. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Tested-By: Benoit Canet <benoit@irqsave.net> Signed-off-by: Kevin Wolf <kwolf@redhat.com>