staging/fwserial: Fix compiler warning

Fix:
drivers/staging/fwserial/fwserial.c:581:3: warning: format '%ld' expects argument of type 'long int', but argument 4 has type 'size_t'

Reported-by: kbuild test robot <[e-mail]>
Signed-off-by: Peter Hurley <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/fwserial/fwserial.c

···
 	size_t size = (n + sizeof(struct buffered_rx) + 0xFF) & ~0xFF;
 
 	if (port->buffered + n > HIGH_WATERMARK) {
-		fwtty_err_ratelimited(port, "overflowed rx buffer: buffered: %d new: %ld wtrmk: %d",
+		fwtty_err_ratelimited(port, "overflowed rx buffer: buffered: %d new: %zu wtrmk: %d",
 				      port->buffered, n, HIGH_WATERMARK);
 		return 0;
 	}