ksmbd: fix unexpectedly changed path in ksmbd_vfs_kern_path_locked

ksmbd: fix unexpectedly changed path in ksmbd_vfs_kern_path_locked

[ Upstream commit 2ac538e40278a2c0c051cca81bcaafc547d61372 ]

When `ksmbd_vfs_kern_path_locked` met an error and it is not the last
entry, it will exit without restoring changed path buffer. But later this
buffer may be used as the filename for creation.

Fixes: c5a709f08d40 ("ksmbd: handle caseless file creation")
Signed-off-by: He Wang <xw897002528@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>