dts: x86: intel: ia32: fix uart reg-shift
dts: x86: intel: ia32: fix uart reg-shift

Platforms that enable UART_NS16550_ACCESS_IOPORT (the case for ia32)
require reg-shift to be zero. Fix this issue introduced in
4c8a8149de0705c9aaa498ae3c228349c9fe9a3e.

Signed-off-by: Gerard Marull-Paretas <bedb45f43a286e49f4dcda039a436b216ae61ef3@nordicsemi.no>

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