hash_string: Fix zero-length case for !DCACHE_WORD_ACCESS

The self-test was updated to cover zero-length strings; the function
needs to be updated, too.

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: George Spelvin <linux@sciencehorizons.net>
Fixes: fcfd2fbf

 ("fs/namei.c: Add hashlen_string() function")
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/namei.c

@@ -1968,11 +1968,11 @@ u64 hashlen_string(const char *name)
 	unsigned long len = 0, c;
 
 	c = (unsigned char)*name;
-	do {
+	while (c) {
 		len++;
 		hash = partial_name_hash(c, hash);
 		c = (unsigned char)name[len];
-	} while (c);
+	}
 	return hashlen_create(end_name_hash(hash), len);
 }
 EXPORT_SYMBOL(hashlen_string);