sscanf(): fix %*s%n

When using %*s, sscanf should honor conversion specifiers immediately
following the %*s.  For example, the following code should find the
position of the end of the string "hello".

  int end;
  char buf[] = "hello    world";
  sscanf(buf, "%*s%n", &end);
  printf("%d\n", end);

Ideally, sscanf would advance the fmt and str pointers the same as it
would without the *, but the code for that is rather complicated and is
not included in the patch.
Signed-off-by: Andy Spencer <andy753421@gmail.com>
Acked-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/vsprintf.c

@@ -1771,7 +1771,7 @@ int vsscanf(const char * buf, const char * fmt, va_list args)
 		 * advance both strings to next white space
 		 */
 		if (*fmt == '*') {
-			while (!isspace(*fmt) && *fmt)
+			while (!isspace(*fmt) && *fmt != '%' && *fmt)
 				fmt++;
 			while (!isspace(*str) && *str)
 				str++;