spi: sprd: Change to use devm_hwspin_lock_request_specific()

Change to use devm_hwspin_lock_request_specific() instead of
freeing the hwlock explicitly when unbound the device.

Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>