Instead of returning an error if the watermark value is too high, which
the core will silently ignore anyway, limit the value to the hardware
FIFO size; a lower-than-requested value is still better than using the
default, which is usually 1.

Cc: Eugen Hristev <eugen.hristev@microchip.com>
Cc: Nicolas Ferre <nicolas.ferre@microchip.com>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20220117102512.31725-2-paul@crapouillou.netSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>