[PATCH for 7.2] minor fixups in block code

[Denis V. Lunev]

These 2 patches are just minor improvements to make code a bit better.

Signed-off-by: Denis V. Lunev <d...@openvz.org>
CC: Kevin Wolf <kw...@redhat.com>
CC: Hanna Reitz <hre...@redhat.com>
CC: Stefan Hajnoczi <stefa...@redhat.com>
CC: Fam Zheng <f...@euphon.net>
CC: Ronnie Sahlberg <ronniesahlb...@gmail.com>
CC: Paolo Bonzini <pbonz...@redhat.com>
CC: Peter Lieven <p...@kamp.de>
CC: Vladimir Sementsov-Ogievskiy <vsement...@yandex-team.ru>