scsi: ibmvfc: Replace deprecated strncpy() with strscpy()

scsi: ibmvfc: Replace deprecated strncpy() with strscpy()

strncpy() is deprecated for use on NUL-terminated destination strings [1]
and as such we should prefer more robust and less ambiguous string
interfaces.

We expect these fields to be NUL-terminated as the property names from
which they are derived are also NUL-terminated.

Moreover, NUL-padding is not required as our destination buffers are
already NUL-allocated and any future NUL-byte assignments are redundant
(like the ones that strncpy() does).
ibmvfc_probe() ->
|       struct ibmvfc_host *vhost;
|       struct Scsi_Host *shost;
...
| 	shost = scsi_host_alloc(&driver_template, sizeof(*vhost));
... **side note: is this a bug? Looks like a type to me   ^^^^^**
...
|	vhost = shost_priv(shost);

... where shost_priv() is:
|       static inline void *shost_priv(struct Scsi_Host *shost)
|       {
|       	return (void *)shost->hostdata;
|       }

.. and:
scsi_host_alloc() ->
| 	shost = kzalloc(sizeof(struct Scsi_Host) + privsize, GFP_KERNEL);

And for login_info->..., NUL-padding is also not required as it is
explicitly memset to 0:
|	memset(login_info, 0, sizeof(*login_info));

Considering the above, a suitable replacement is strscpy() [2] due to
the fact that it guarantees NUL-termination on the destination buffer
without unnecessarily NUL-padding.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
Link: https://github.com/KSPP/linux/issues/90
Cc: <linux-hardening@vger.kernel.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
Link: https://lore.kernel.org/r/20231030-strncpy-drivers-scsi-ibmvscsi-ibmvfc-c-v1-1-5a4909688435@google.com
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>