tty: serial: fsl_lpuart: use UARTMODIR register bits for lpuart32 platform

For lpuart32 platforms, UARTMODIR register is used instead of UARTMODEM.
So here should configure the corresponding UARTMODIR register bits to
avoid confusion.

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
Link: https://lore.kernel.org/r/20230414022111.20896-1-sherry.sun@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>