thermal: intel: int340x_thermal: 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.

psvt->limit.string can only be 8 bytes so let's use the appropriate size
macro ACPI_LIMIT_STR_MAX_LEN.

Neither psvt->limit.string or psvt_user[i].limit.string requires the
NUL-padding behavior that strncpy() provides as they have both been
filled with NUL-bytes prior to the string operation.
|	memset(&psvt->limit, 0, sizeof(u64));
and
| 	psvt_user = kzalloc(psvt_len, GFP_KERNEL);

Let's use `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 # [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90


Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>