MAINTAINERS: Add myself as openrisc maintainer

Jia has claimed he is no longer able to maintain.  I have fixing bugs here
and there and getting familiar with the code base. Orignal thread from Jia:

 https://lists.librecores.org/pipermail/openrisc/2017-January/000321.html

Signed-off-by: Stafford Horne <shorne@gmail.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

MAINTAINERS

@@ -196,8 +196,8 @@ F: hw/nios2/
 F: disas/nios2.c
 
 OpenRISC
-M: Jia Liu <proljc@gmail.com>
-S: Maintained
+M: Stafford Horne <shorne@gmail.com>
+S: Odd Fixes
 F: target/openrisc/
 F: hw/openrisc/
 F: tests/tcg/openrisc/