common: unknown hash type of judgment modification

common: unknown hash type of judgment modification

ceph_str_hash() return -1 if set unknown hash type
but (unsiged)-1 = unsiged 4294967295
So we can't judge whether the 4294967295 is the normal value of hash, or the return value of the unknown hash type
use ceph_str_hash_valid() verify the hash type before generating the hash value

Signed-off-by: huanwen ren <ren.huanwen@zte.com.cn>