spi: spi-fsl-qspi: use devm_spi_register_controller

The driver does not clearly unregister the spi controller.
Therefore calling an unbind and bind again will end up in a
Kernel crash.

The function devm_spi_register_controller will automatically
be unregister the SPI device.

Signed-off-by: Volker Haspel <volker.haspel@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>