tty: serial: fsl_lpuart: Use u32 and u8 for register variables

Use u32 and u8 rather than unsigned long or unsigned char for register
variables for clarity and consistency.

Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
Link: https://lore.kernel.org/r/20250312023904.1343351-2-sherry.sun@nxp.com


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