serial: core: move sanitizing of RS485 delays into own function

Move the sanitizing of RS485 delays out of uart_sanitize_serial_rs485()
into the new function uart_sanitize_serial_rs485_delays().

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Lino Sanfilippo <l.sanfilippo@kunbus.com>
Link: https://lore.kernel.org/r/20220710164442.2958979-5-LinoSanfilippo@gmx.de


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