ksmbd: fix an oops in error handling in smb2_open()

If smb2_get_name() then name is an error pointer.  In the clean up
code, we try to kfree() it and that will lead to an Oops.  Set it to
NULL instead.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Steve French <stfrench@microsoft.com>