meta/lib/oe/rootfs.py: Fix typo "Restoreing" -> "Restoring"

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 2621dbbc)
Signed-off-by: Steve Sakoman <steve@sakoman.com>