i2c-mpc: bug fix for MPC52xx clock setting and printout

The clock setting did not work for the MPC52xx due to a stupid bug.
Furthermore, the dev info output "clock=0" for old device trees was
misleading. This patch fixes both issues.

Signed-off-by: Wolfgang Grandegger <wg@grandegger.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>