CMD: random: fix return code

As of today 'random' command return 1 (CMD_RET_FAILURE) in case
of successful execution and 0 (CMD_RET_SUCCESS) in case of bad
arguments. Fix that.

NOTE: we remove printing usage information from command body
so it won't print twice.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/mem.c b/cmd/mem.c
index 0bfb608..009b7b5 100644
--- a/cmd/mem.c
+++ b/cmd/mem.c
@@ -1144,10 +1144,8 @@
 	unsigned char *buf8;
 	unsigned int i;
 
-	if (argc < 3 || argc > 4) {
-		printf("usage: %s <addr> <len> [<seed>]\n", argv[0]);
-		return 0;
-	}
+	if (argc < 3 || argc > 4)
+		return CMD_RET_USAGE;
 
 	len = simple_strtoul(argv[2], NULL, 16);
 	addr = simple_strtoul(argv[1], NULL, 16);
@@ -1174,7 +1172,8 @@
 
 	unmap_sysmem(start);
 	printf("%lu bytes filled with random data\n", len);
-	return 1;
+
+	return CMD_RET_SUCCESS;
 }
 #endif