MAINTAINERS: Update PPC status and maintainer

Richard agreed to make odd fixes to PPC tcg parts[1]. This patch makes
the change.

[1] https://lists.gnu.org/archive/html/qemu-ppc/2016-03/msg00657.htmlSigned-off-by: NPranith Kumar <bobby.prani@gmail.com>
Signed-off-by: NRichard Henderson <rth@twiddle.net>

MAINTAINERS

@@ -1504,8 +1504,8 @@ F: tcg/mips/
 F: disas/mips.c
 
 PPC
-M: Vassili Karpov (malc) <av1474@comtv.ru>
-S: Maintained
+M: Richard Henderson <rth@twiddle.net>
+S: Odd Fixes
 F: tcg/ppc/
 F: disas/ppc.c