firmware-utils/buffalo-enc: explicitly use signed char for checksum function

ARM defaults to unsigned char and that breaks the calculation, as it
relies on sign extension

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

SVN-Revision: 47186

tools/firmware-utils/src/buffalo-lib.c

@@ -179,7 +179,7 @@ int bcrypt_buf(unsigned char seed, unsigned char *key, unsigned char *src,
 
 uint32_t buffalo_csum(uint32_t csum, void *buf, unsigned long len)
 {
-	char *p = buf;
+	signed char *p = buf;
 
 	while (len--) {
 		int i;