[U-Boot] compiler warning associated with noreturn

[Kumar Gala]

With the following commit:

commit d2e8b911c0a0661d395ccac72156040702ac842d
Author: Mike Frysinger <vapier at gentoo.org>
Date:   Wed Jun 29 11:58:04 2011 +0000

    panic: add noreturn attribute

we now get warnings like the following if we build MPC8540ADS_config:

vsprintf.c: In function 'panic':
vsprintf.c:730:1: warning: 'noreturn' function does return

Seems like do_reset() needs a similar attribute?  Or some other change?

- k