tty: serial: fsl_lpuart: Use pm_ptr() to avoid need to make pm __maybe_unused

Use pm_ptr() to remove the need to mark the pm functions as
__maybe_unused when the kernel is built without CONFIG_PM support.

Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
Link: https://lore.kernel.org/r/20221110113859.8485-4-sherry.sun@nxp.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>