serial: fsl_lpuart: Remove custom frame size calculation

serial: fsl_lpuart: Remove custom frame size calculation

The number of bits can be calculated using tty_get_frame_size(), no
need for the driver to do it on its own. Change bits to unsigned and
baud too since we're touching the declarations line anyway (the
respective core functions are typed unsigned).

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220830084925.5608-4-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>