package/petitboot: fix HOST_PROG_SHUTDOWN value

HOST_PROG_SHUTDOWN currently references a file that doesn't exist. Fix
by setting it to /usr/libexec/petitboot/bb-kexec-reboot, which this
package already installs but doesn't use.

Signed-off-by: Reza Arbab <arbab@linux.ibm.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>
(cherry picked from commit ab91ddd8a8ebdc10fa26a6d9541cf5e50e297973)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/petitboot/petitboot.mk

@@ -21,7 +21,7 @@ PETITBOOT_CONF_OPTS = \
 	--without-twin-x11 \
 	$(if $(BR2_PACKAGE_BUSYBOX),--enable-busybox,--disable-busybox) \
 	HOST_PROG_KEXEC=/usr/sbin/kexec \
-	HOST_PROG_SHUTDOWN=/usr/sbin/kexec-restart
+	HOST_PROG_SHUTDOWN=/usr/libexec/petitboot/bb-kexec-reboot
 
 # HPA and Busybox tftp are supported. HPA tftp is part of Buildroot's tftpd
 # package.