drivers: serial: Fix mcux lpuart instance 2
drivers: serial: Fix mcux lpuart instance 2

The mcux lpuart shim driver was updated in commit
20202902f2a8210497736dd872c539abf9a9a424 to use DT_ prefix in all
defined labels not related to Kconfig, but instance 2 was missed.

Signed-off-by: Maureen Helm <87a696db5547fa477bda9f9e0f00013c839c14d3@nxp.com>

GiulianoFranchetto/zephyr,nashif/zephyr,Vudentz/zephyr,explora26/zephyr,Vudentz/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,explora26/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,finikorg/zephyr,finikorg/zephyr,nashif/zephyr,galak/zephyr,finikorg/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,Vudentz/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,finikorg/zephyr,galak/zephyr,explora26/zephyr,nashif/zephyr,ldts/zephyr,explora26/zephyr,ldts/zephyr,nashif/zephyr,explora26/zephyr,galak/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr