tty: serial: fsl_lpuart: increase maximum uart_nr to 12

Some SoCs like the i.MX943 have aliases for up to 12 UARTs, need to
increase UART_NR from 8 to 12 to support lpuart9-12 to avoid
initialization failures.

Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
Link: https://lore.kernel.org/r/20250103071154.3070924-1-sherry.sun@nxp.com


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