powerpc/85xx: Don't report SRAM to L2 cache fallback as error

If the SRAM region parameters are missing the SRAM driver
probing exits and the L2 region is configured as L2 cache
entirely.  This is the expected default behaviour, so it
makes no sense to report it as an error.

Signed-off-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Signed-off-by: Scott Wood <oss@buserror.net>