spi: spi-fsl-dspi: Replace legacy spi_master names with spi_controller

This adapts the spi-fsl-dspi driver to the API changes introduced in
commit 8caab75f

 ("spi: Generalize SPI "master" to "controller"").

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/20190818180115.31114-10-olteanv@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>