Fix bogus opost buffer size check

Noted while going through the n_tty code: that buffer check
used to check against the size of the temporary kernel buffer,
but since the tty layer was changed to use kernel buffers
though-out, the kernel buffer array became just a pointer, and
the check was limiting the opost blocksize to the size of a
pointer, which makes no sense.

Just remove it, since now the whole buffer is always in kernel
space.

drivers/char/n_tty.c

@@ -317,8 +317,6 @@ static ssize_t opost_block(struct tty_struct * tty,
 		return 0;
 	if (nr > space)
 		nr = space;
-	if (nr > sizeof(buf))
-	    nr = sizeof(buf);
 
 	for (i = 0, cp = buf; i < nr; i++, cp++) {
 		switch (*cp) {