drivers: serial: ns16550: fix uart initialization
drivers: serial: ns16550: fix uart initialization

Do not set DLAB bit in Line Control Register when the access to
the baud rate divisor registers is not needed.

Signed-off-by: Dawid Niedzwiecki <73bc8c219b84b29e82d4338ec2e55b540c845bc6@semihalf.com>

finikorg/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,galak/zephyr