scsi: lpfc: 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 ae->value_string to be NUL-terminated because there's a comment
that says as much; these attr strings are also used with other string APIs,
further cementing the fact.

Now, the question of whether or not to NUL-pad the destination buffer:
lpfc_fdmi_rprt_defer() initializes vports (all zero-initialized), then we
call lpfc_fdmi_cmd() with each vport and a mask. Then, inside of
lpfc_fdmi_cmd() we check each bit in the mask to invoke the proper
callback. Importantly, the zero-initialized vport is passed in as the
"attr" parameter. Seeing this:
| struct lpfc_fdmi_attr_string *ae = attr;
... we can tell that ae->value_string is entirely zero-initialized. Due
to this, NUL-padding is _not_ required as it would be redundant.

Considering the above, a suitable replacement is strscpy() [2].

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: [e-mail]
Signed-off-by: Justin Stitt <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Kees Cook <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/lpfc/lpfc_ct.c

···
 	 * 64 bytes or less.
 	 */
 
-	strncpy(ae->value_string, attrstring, sizeof(ae->value_string));
+	strscpy(ae->value_string, attrstring, sizeof(ae->value_string));
 	len = strnlen(ae->value_string, sizeof(ae->value_string));
-	/* round string length to a 32bit boundary. Ensure there's a NULL */
+	/* round string length to a 32bit boundary */
 	len += (len & 3) ? (4 - (len & 3)) : 4;
 	/* size is Type/Len (4 bytes) plus string length */
 	size = FOURBYTES + len;