btrfs: initialize fs_devices->fs_info earlier in btrfs_init_devices_late()

btrfs: initialize fs_devices->fs_info earlier in btrfs_init_devices_late()

Currently, fs_devices->fs_info is initialized in btrfs_init_devices_late(),
but this occurs too late for find_live_mirror(), which is invoked by
load_super_root() much earlier than btrfs_init_devices_late().

Fix this by moving the initialization to open_ctree(), before load_super_root().

Reviewed-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>