MAINTAINERS: update sboyd's email address

Replace my codeaurora.org address with my kernel.org address so that
emails don't bounce.

Link: http://lkml.kernel.org/r/20180129173258.10643-1-sboyd@codeaurora.org


Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>