ppc4xx: Fix printf format warnings now visible with the updated format check

This patch fixes ppc4xx related printf format warning. Those warnings are
now visible since patch dc4b0b38d4aadf08826f6c31270f1eecd27964fd
[Fix printf errors.] by Andrew Klossner has been applied. Thanks, this is
really helpful.

Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/cpu/ppc4xx/4xx_enet.c b/cpu/ppc4xx/4xx_enet.c
index c40e0ca..4e863dc 100644
--- a/cpu/ppc4xx/4xx_enet.c
+++ b/cpu/ppc4xx/4xx_enet.c
@@ -1076,7 +1076,7 @@
 
 		bd_cached = (u32)malloc_aligned(MAL_ALLOC_SIZE, 4096);
 		if (!bd_cached) {
-			printf("%s: Error allocating MAL descriptor buffers!\n");
+			printf("%s: Error allocating MAL descriptor buffers!\n", __func__);
 			return -1;
 		}