ppc4xx: Fix spelling error in MAINTAINERS file

Signed-off-by: Stefan Roese <sr@denx.de>

MAINTAINERS

@@ -319,8 +319,8 @@ Ricardo Ribalda <ricardo.ribalda@uam.es>
 
 	ml507 		PPC440x5
 	v5fx30teval	PPC440x5
-	xilinx-pp440-generic	PPC440x5
-	xilinx-pp405-generic	PPC405
+	xilinx-ppc405-generic	PPC405
+	xilinx-ppc440-generic	PPC440x5
 
 Stefan Roese <sr@denx.de>