MXC: Correct SPI_CPOL setting in SPI driver

The handling of the SPI_CPOL bit inside the SPI
driver was wrong. As reported by the manual,
the meaning of the SSPOL inside the
configuration register is the same as reported
by SPI specification (0 if low in idle, 1 is high
on idle). The driver inverts this logic.

Because this patch sets the logic as specified, it is required
to clear the CPOL bit in the configuration file to adapt
to the correct logic.

Signed-off-by: Stefano Babic <sbabic@denx.de>
Signed-off-by: David Jander <david.jander@protonic.nl>