adfs: fix filename handling

Fix filenames on adfs discs being terminated at the first character greater
than 128 (adfs filenames are Latin 1).  I saw this problem when using a
loopback adfs image on a 2.6.17-rc5 x86_64 machine, and the patch fixed it
there.
Signed-off-by: Adrian Bunk <bunk@stusta.de>

fs/adfs/dir_f.c

@@ -53,7 +53,7 @@ static inline int adfs_readname(char *buf, char *ptr, int maxlen)
 {
 	char *old_buf = buf;
 
-	while (*ptr >= ' ' && maxlen--) {
+	while ((unsigned char)*ptr >= ' ' && maxlen--) {
 		if (*ptr == '/')
 			*buf++ = '.';
 		else