cacheinfo: Return error code in init_of_cache_level()

Make init_of_cache_level() return an error code when the cache
information parsing fails to help detecting missing information.

init_of_cache_level() is only called for riscv. Returning an error
code instead of 0 will prevent detect_cache_attributes() to allocate
memory if an incomplete DT is parsed.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>