spi: s3c64xx: fix inconsistency between binding and driver

Commit a92e7c3d ("spi: s3c64xx: consider the case when the CS
line is not connected") introduced an inconsistency between the
binding, where the disconnected CS line was marked as
'no-cs-readback', and the driver.

The driver is erroneously checking for that attribute with
property name of 'broken-cs'.

Check for 'no-cs-readback' in the driver as well.

Fixes: a92e7c3d ("spi: s3c64xx: consider the case when the CS line is not connected")
Signed-off-by: Andi Shyti <andi.shyti@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org