MAINTAINERS: Add reviewer for XIVE

Fred discusses frequently with the IBM HW designers, he is fluent in
XIVE logic, add him as a reviewer.

Cc: Frédéric Barrat <fbarrat@linux.ibm.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Acked-by: Frederic Barrat <fbarrat@linux.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

MAINTAINERS

@@ -2448,6 +2448,7 @@ T: git https://github.com/philmd/qemu.git fw_cfg-next
 
 XIVE
 M: Cédric Le Goater <clg@kaod.org>
+R: Frédéric Barrat <fbarrat@linux.ibm.com>
 L: qemu-ppc@nongnu.org
 S: Odd Fixes
 F: hw/*/*xive*