spi: nxp-fspi: Use devm API to fix missed unregistration of controller

This driver forgets to unregister controller when remove.
Use devm API to unregister it automatically to fix it.

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Link: https://lore.kernel.org/r/20191109075517.29988-1-hslester96@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>