net/atm: fix proc_mpc_write incorrect return value

Then the input contains '\0' or '\n', proc_mpc_write has read them,
so the return value needs +1.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Xiaobo Liu <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/atm/mpoa_proc.c

···
 	if (!page)
 		return -ENOMEM;
 
-	for (p = page, len = 0; len < nbytes; p++, len++) {
+	for (p = page, len = 0; len < nbytes; p++) {
 		if (get_user(*p, buff++)) {
 			free_page((unsigned long)page);
 			return -EFAULT;
 		}
+		len += 1;
 		if (*p == '\0' || *p == '\n')
 			break;
 	}