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>