Fix compiler warning in mpc8xxx ddr code

ctrl_regs.c: In function 'compute_fsl_memctl_config_regs':
ctrl_regs.c:523: warning: 'caslat' may be used uninitialized in this function
ctrl_regs.c:523: note: 'caslat' was declared here

Add a warning in DDR1 case if cas_latency isn't a value we know about.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>