Some filesystems (like cd9660 and ext3) require that VFS_STATFS()
be called before VFS_ROOT() is called. Move the call for VFS_STATFS()
so that it is done after VFS_MOUNT(), but before VFS_ROOT().
This change actually improves the robustness of the mount system
call because it returns an error rather than failing silently
when VFS_STATFS() returns failure.

Reported by: Rebecca Cran <rebecca@bluestop.org>
Sponsored by: Netflix