spi: rspi: use platform drvdata correctly in rspi_remove()

We had set the platform drvdata in rspi_probe() as a type of
struct rspi_data, but use it as struct spi_master in rspi_remove()
Fix by remove the unnecessary spi_master_[get|put]() since rspi->master
is no longer used after spi_unregister_master().

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Mark Brown <broonie@linaro.org>