MAINTAINERS: change Sparse's maintainer

I'm taking over the maintainance of Sparse so add myself as
maintainer and move Christopher's info to CREDITS.

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

CREDITS

@@ -2204,6 +2204,10 @@ S: Post Office Box 371
 S: North Little Rock, Arkansas 72115
 S: USA
 
+N: Christopher Li
+E: sparse@chrisli.org
+D: Sparse maintainer 2009 - 2018
+
 N: Stephan Linz
 E: linz@mazet.de
 E: Stephan.Linz@gmx.de