lib: fix scnprintf() if @size is == 0

scnprintf() should return 0 if @size is == 0. Update the comment for it,
as @size is unsigned.

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/vsprintf.c

@@ -1504,7 +1504,7 @@ EXPORT_SYMBOL(snprintf);
  * @...: Arguments for the format string
  *
  * The return value is the number of characters written into @buf not including
- * the trailing '\0'. If @size is <= 0 the function returns 0.
+ * the trailing '\0'. If @size is == 0 the function returns 0.
  */
 
 int scnprintf(char *buf, size_t size, const char *fmt, ...)
@@ -1516,7 +1516,11 @@ int scnprintf(char *buf, size_t size, const char *fmt, ...)
 	i = vsnprintf(buf, size, fmt, args);
 	va_end(args);
 
-	return (i >= size) ? (size - 1) : i;
+	if (likely(i < size))
+		return i;
+	if (size != 0)
+		return size - 1;
+	return 0;
 }
 EXPORT_SYMBOL(scnprintf);