Merge remote-tracking branch 'remotes/ericb/tags/pull-bitmaps-2020-10-26' into staging

bitmaps patches for 2020-10-26

- fix infloop on large bitmap granularity
- silence compiler warning

# gpg: Signature made Mon 26 Oct 2020 11:56:54 GMT
# gpg:                using RSA key 71C2CC22B1C4602927D2F3AAA7A16B4A2527436A
# gpg: Good signature from "Eric Blake <eblake@redhat.com>" [full]
# gpg:                 aka "Eric Blake (Free Software Programmer) <ebb9@byu.net>" [full]
# gpg:                 aka "[jpeg image of size 6874]" [full]
# Primary key fingerprint: 71C2 CC22 B1C4 6029 27D2  F3AA A7A1 6B4A 2527 436A

* remotes/ericb/tags/pull-bitmaps-2020-10-26:
  migration/block-dirty-bitmap: fix uninitialized variable warning
  migration/block-dirty-bitmap: fix larger granularity bitmaps

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>