ksmbd: remove generic_fillattr use in smb2_open()

Removed the use of unneeded generic_fillattr() in smb2_open().

Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>