MAINTAINERS: Add fw_cfg.c to PPC mac99 machine

The hw/ppc/fw_cfg.c file contains the implementation of
fw_cfg_arch_key_name(), used by the common nvram model. List it under
mac99 machine next to the mac_nvram model.

Cc: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
diff --git a/MAINTAINERS b/MAINTAINERS
index 303f4c7..543a6be 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1410,6 +1410,7 @@
 F: hw/misc/macio/
 F: hw/misc/mos6522.c
 F: hw/nvram/mac_nvram.c
+F: hw/ppc/fw_cfg.c
 F: hw/input/adb*
 F: include/hw/misc/macio/
 F: include/hw/misc/mos6522.h