tty: atmel_serial: update outdated reference to atmel_tasklet_func()

The modem-status comparison that used irq_status_prev was
moved from atmel_tasklet_func() into atmel_handle_status() in
commit d033e82db9 ("tty/serial: at91: handle IRQ status
more safely").  Update the comment accordingly.

Assisted-by: unnamed:deepseek-v3.2 coccinelle
Signed-off-by: Kexin Sun <kexinsun@smail.nju.edu.cn>
Link: https://patch.msgid.link/20260324024857.3244-1-kexinsun@smail.nju.edu.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/atmel_serial.c

@@ -1927,7 +1927,7 @@ static int atmel_startup(struct uart_port *port)
 		atmel_uart_writel(port, ATMEL_US_FMR, fmr);
 	}
 
-	/* Save current CSR for comparison in atmel_tasklet_func() */
+	/* Save current CSR for comparison in atmel_handle_status() */
 	atmel_port->irq_status_prev = atmel_uart_readl(port, ATMEL_US_CSR);
 
 	/*