fix compat_sys_rt_sigprocmask()

Converting bitmask to 32bit granularity is fine, but we'd better
_do_ something with the result.  Such as "copy it to userland"...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

kernel/signal.c

@@ -2653,7 +2653,7 @@ COMPAT_SYSCALL_DEFINE4(rt_sigprocmask, int, how, compat_sigset_t __user *, nset,
 	if (oset) {
 		compat_sigset_t old32;
 		sigset_to_compat(&old32, &old_set);
-		if (copy_to_user(oset, &old_set, sizeof(sigset_t)))
+		if (copy_to_user(oset, &old32, sizeof(compat_sigset_t)))
 			return -EFAULT;
 	}
 	return 0;