serial: core: sanitize RS485 delays read from device tree

serial: core: sanitize RS485 delays read from device tree

Currently the RTS delays set via device tree are not clamped to a maximum
value although the device tree bindings documentation for RS485 claims that
only a maximum of 1000 msecs is allowed.

So clamp the values to avoid arbitrary high delay settings. However clamp
the values to 100 instead of 1000 msecs to be consistent which the maximum
that is allowed when setting the delays from userspace via the UART ioctl
TIOCSRS485.

Signed-off-by: Lino Sanfilippo <l.sanfilippo@kunbus.com>
Link: https://lore.kernel.org/r/20220710164442.2958979-6-LinoSanfilippo@gmx.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>