security: Fix ret values doc for security_inode_init_security()

Commit 6bcdfd2c ("security: Allow all LSMs to provide xattrs for
inode_init_security hook") unified the !initxattrs and initxattrs cases. By
doing that, security_inode_init_security() cannot return -EOPNOTSUPP
anymore, as it is always replaced with zero at the end of the function.

Also, mentioning -ENOMEM as the only possible error is not correct. For
example, evm_inode_init_security() could return -ENOKEY.

Fix these issues in the documentation of security_inode_init_security().

Fixes: 6bcdfd2c ("security: Allow all LSMs to provide xattrs for inode_init_security hook")
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/security.c

@@ -1604,8 +1604,8 @@ EXPORT_SYMBOL(security_dentry_create_files_as);
  * a security attribute on this particular inode, then it should return
  * -EOPNOTSUPP to skip this processing.
  *
- * Return: Returns 0 on success, -EOPNOTSUPP if no security attribute is
- * needed, or -ENOMEM on memory allocation failure.
+ * Return: Returns 0 if the LSM successfully initialized all of the inode
+ *         security attributes that are required, negative values otherwise.
  */
 int security_inode_init_security(struct inode *inode, struct inode *dir,
 				 const struct qstr *qstr,