ARM: imx51: use platform id 2 for imx51-cspi

The platform id is used to determine the spi bus number, so it should
better be different to the ids used for imx51-ecspi.  Otherwise it's not
possible to use both devices "imx51-cspi.0" and "imx51-ecspi.0".

Alternative approaches are to use dynamic bus numbering as offered by
the spi framework or let the machine code set the bus number.  The
downside of both possibilities is that the bus number isn't fixed for
the same busses on different machines using i.MX51.

LAKML-Reference: 1302100716-21034-1-git-send-email-u.kleine-koenig@pengutronix.de
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>