initramfs-framework/setup-live: fix shebang

Signed-off-by: Ulrich Ölmann <u.oelmann@pengutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 71f1f6bc)
Signed-off-by: Steve Sakoman <steve@sakoman.com>