FAT: use toupper/tolower instead of recoding them

toupper/tolower function are already declared, so use them.

Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Acked-by: Marek Vasut <marex@denx.de>
Acked-by: Stefano Babic <sbabic@denx.de>
diff --git a/fs/fat/fat_write.c b/fs/fat/fat_write.c
index 4a1bda0..819c33b 100644
--- a/fs/fat/fat_write.c
+++ b/fs/fat/fat_write.c
@@ -28,6 +28,7 @@
 #include <fat.h>
 #include <asm/byteorder.h>
 #include <part.h>
+#include <linux/ctype.h>
 #include "fat.c"
 
 static void uppercase(char *str, int len)
@@ -35,7 +36,7 @@
 	int i;
 
 	for (i = 0; i < len; i++) {
-		TOUPPER(*str);
+		*str = toupper(*str);
 		str++;
 	}
 }