VFS: provide correct root directory for lookups
VFS: provide correct root directory for lookups

This fixes a VFS panic and a chroot(2) security hole.

Change-Id: Ifd1923f886501cf3a73277aab89db974798c47dc

veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi