amiserial: Drop duplicate NULL check in shutdown()

The free_page(addr), which becomes free_pages(addr, 0) checks addr
against 0. No need to repeat this check in the caller.
Acked-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220202165655.5647-1-andriy.shevchenko@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/amiserial.c

@@ -538,10 +538,8 @@ static void shutdown(struct tty_struct *tty, struct serial_state *info)
 	 */
 	free_irq(IRQ_AMIGA_VERTB, info);
 
-	if (info->xmit.buf) {
-		free_page((unsigned long) info->xmit.buf);
-		info->xmit.buf = NULL;
-	}
+	free_page((unsigned long)info->xmit.buf);
+	info->xmit.buf = NULL;
 
 	info->IER = 0;
 	amiga_custom.intena = IF_RBF | IF_TBE;