ksmbd: fix control flow issues in sid_to_id()

Addresses-Coverity reported Control flow issues in sid_to_id()
/fs/ksmbd/smbacl.c: 277 in sid_to_id()
271
272	if (sidtype == SIDOWNER) {
273		kuid_t uid;
274		uid_t id;
275
276		id = le32_to_cpu(psid->sub_auth[psid->num_subauth - 1]);
>>>	CID 1506810:  Control flow issues  (NO_EFFECT)
>>>	This greater-than-or-equal-to-zero comparison of an unsigned value
>>>	is always true. "id >= 0U".
277		if (id >= 0) {
278			/*
279			 * Translate raw sid into kuid in the server's user
280			 * namespace.
281			 */
282			uid = make_kuid(&init_user_ns, id);

Addresses-Coverity: ("Control flow issues")
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>