serial: ucc_uart: Remove custom frame size calculation

serial: ucc_uart: 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.

Also remove a comment on number of bits that doesn't match the code nor
the comment on ucc_uart_pram's rx_length ("minus 1" part differs). That
comment seems a verbatim copy of that in cpm_uart/cpm_uart_core.c
anyway so perhaps it was just copied over w/o much thinking.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220830084925.5608-2-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>