MAINTAINERS: Move the Freescale QSPI driver to the SPI framework

The driver was ported to the SPI framework so it can be used as
a generic SPI memory driver and not only for SPI NOR.
Reflect this transition in the MAINTAINERS file.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Mark Brown <broonie@kernel.org>