nvme-fabrics: fix DHCHAP secret leak on parse failure

In the Linux kernel, the following vulnerability has been resolved:

nvme-fabrics: fix DHCHAP secret leak on parse failure

nvmf_parse_options() duplicates dhchap_secret and dhchap_ctrl_secret
with match_strdup() before validating the DHHC-1: representation.

If validation fails, the parser returns -EINVAL before the temporary
string in p is assigned to opts->dhchap_secret or
opts->dhchap_ctrl_secret. nvmf_create_ctrl() subsequently frees opts,
but nvmf_free_options() cannot release the unassigned temporary string.
Each rejected option therefore leaks one allocation.

This is easy to miss because valid secrets transfer ownership to opts
and are freed normally, while the malformed-secret path still returns
the expected -EINVAL to userspace.

With CONFIG_NVME_HOST_AUTH enabled, the leak is reachable before the
required-option checks and transport lookup. No NVMe-oF target or
working transport connection is required; for example, repeatedly
writing

dhchap_secret=BAD

or

dhchap_ctrl_secret=BAD

to /dev/nvme-fabrics deterministically takes the leaking parse path.

Free the temporary string before leaving both validation error paths.
Use kfree_sensitive() because the copied option may contain secret
material even when its representation is rejected, matching the
sensitive cleanup used for stored DHCHAP secrets.