spi: imx: Improve driver description

"SPI Controller driver" is a too generic description.

Make it i.MX specific instead.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20210316180922.239805-1-festevam@gmail.com


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