virtio-blk logical block size should never be larger than physical block
size because it doesn't make sense to have such configurations. QEMU doesn't
have a way to effectively express this condition; the best it can do is
report the physical block exponent as 0 - indicating the logical block size
equals the physical block size.

This is identical to commit 3da023b5
but applied to virtio-blk (instead of virtio-scsi).
Signed-off-by: NMark Kanda <mark.kanda@oracle.com>
Reviewed-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: NAmeya More <ameya.more@oracle.com>
Reviewed-by: NMartin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Message-id: 773169891f9f2deb4cb7c4ef2655580dbe24c1d1.1513005190.git.mark.kanda@oracle.com
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>