fs/adfs/adfs.h: fix unsigned comparison

fs/adfs/adfs.h: In function 'append_filetype_suffix':
fs/adfs/adfs.h:115: warning: comparison is always false due to limited range of data type
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Stuart Swales <stuart.swales.croftnuisk@gmail.com>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/adfs/adfs.h

@@ -112,7 +112,7 @@ struct object_info {
 /* RISC OS 12-bit filetype converts to ,xyz hex filename suffix */
 static inline int append_filetype_suffix(char *buf, __u16 filetype)
 {
-	if (filetype == -1)
+	if (filetype == 0xffff)	/* no explicit 12-bit file type was set */
 		return 0;
 
 	*buf++ = ',';