fs/smb/client: Reset password pointer to NULL

jira VULN-9356
cve CVE-2023-5345
commit-author Quang Le <[email protected]>
commit e6e43b8
upstream-diff The mainline `e6e43b8a' commit consisting of a single line
              `ctx->password = NULL' is a fix of commit
              `a4e430c8c8ba96be8c6ec4f2eb108bb8bcbee069' (not mentioned
              anywhere), whose erroneous code is not present in `ciqlts9_2-rt',
              so the fix doesn't apply. The `a4e430c8' commit can be treated as
              a vulnerability patch itself (erasing passwords stored on heap
              upon freeing, thus ensuring that no secrets linger in
              RAM). However, it's not a part of CVE-2023-5345, or any other CVE
              for that matter.

Forget to reset ctx->password to NULL will lead to bug like double free

        Cc: [email protected]
        Cc: Willy Tarreau <[email protected]>
        Reviewed-by: Namjae Jeon <[email protected]>
        Signed-off-by: Quang Le <[email protected]>
        Signed-off-by: Steve French <[email protected]>
(cherry picked from commit e6e43b8)
        Signed-off-by: Marcin Wcisło <[email protected]>

Author: pvts-mat