serial: 8250_aspeed_vuart: Switch to use uart_read_port_properties()

Since we have now a common helper to read port properties
use it instead of sparse home grown solution.

Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Andrew Jeffery <andrew@codeconstruct.com.au>
Link: https://lore.kernel.org/r/20240304123035.758700-5-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>