ksmbd: Fix resource leak in smb2_lock()

"flock" is leaked if an error happens before smb2_lock_init(), as the
lock is not added to the lock_list to be cleaned up.

Signed-off-by: Marios Makassikis <mmakassikis@freebox.fr>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>