UPSTREAM: spi: rockchip: covert rsd_nsecs to u32 type

UPSTREAM: spi: rockchip: covert rsd_nsecs to u32 type

rsd_nsecs is defined as u8 memeber of struct rockchip_spi,
but using of_property_read_u32. That means we take risk of
truncation by type conversion if we pass on big value from
dt.

Change-Id: I4d3e29b64749ac8a86782413d0f41691b9ff4e84
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>
(cherry picked from git.kernel.org next/linux-next.git master
 commit 108b5c8bba6be101100596bf37a165214e1c8458)