btrfs-progs: mkfs: Round device size down to sectorsize

btrfs-progs: mkfs: Round device size down to sectorsize

When do following command in a vm, whose disks are created by
qemu-img create -f raw 11 2.6G:
 # mkfs.btrfs -f /dev/vdd /dev/vde /dev/vdf
 # btrfs-show-super /dev/vdd /dev/vde /dev/vdf | grep dev_item.total_bytes
 dev_item.total_bytes    2791727104
 dev_item.total_bytes    2791729152
 dev_item.total_bytes    2791729152
We can see that the first device's size is little smaller.

And it fails xfstests btrfs/011.

Reason:
 First device's size is rounded down to sectorsize in make_btrfs(),
 but other devices are not.

Fix:
 Round down remain devices' size in btrfs_add_to_fsid().

Reported-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>