spi: mediatek: skip delays if they are 0

In the function 'mtk_spi_set_hw_cs_timing'
the 'setup', 'hold' and 'inactive' delays are configured.
In case those values are 0 it causes errors on mt8173:

cros-ec-i2c-tunnel 1100a000.spi:ec@0:i2c-tunnel0:
	Error transferring EC i2c message -71
cros-ec-spi spi0.0: EC failed to respond in time.

This patch fixes that issues by setting only the values
that are not 0.

Fixes: 04e6bb0d ("spi: modify set_cs_timing parameter")
Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Link: https://lore.kernel.org/r/20211001152153.4604-1-dafna.hirschfeld@collabora.com


Signed-off-by: Mark Brown <broonie@kernel.org>