spi: rockchip: Fix error in getting num-cs property

stable inclusion
from stable-v5.10.106
commit 889254f98e99f824abc76c8fcac5652e140255c3
bugzilla: https://gitee.com/openeuler/kernel/issues/I573US

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=889254f98e99f824abc76c8fcac5652e140255c3



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[ Upstream commit 9382df0a ]

Get num-cs u32 from dts of_node property rather than u16.

Signed-off-by: Jon Lin <jon.lin@rock-chips.com>
Link: https://lore.kernel.org/r/20220216014028.8123-2-jon.lin@rock-chips.com


Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Yu Liao <liaoyu15@huawei.com>
Reviewed-by: Wei Li <liwei391@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>