Fix compiler warnings for ARM systems.

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/board/pleb2/flash.c b/board/pleb2/flash.c
index 97271d9..5a1eba6 100644
--- a/board/pleb2/flash.c
+++ b/board/pleb2/flash.c
@@ -196,7 +196,7 @@
 	int i;
 	uchar *boottype;
 	uchar *bootletter;
-	uchar *fmt;
+	char *fmt;
 	uchar botbootletter[] = "B";
 	uchar topbootletter[] = "T";
 	uchar botboottype[] = "bottom boot sector";