thermal: sysfs: Replace snprintf() with strscpy() in policy_store()

thermal: sysfs: Replace snprintf() with strscpy() in policy_store()

There is no need to use snprintf() with a format specifier to copy 'buf'
to 'name'; use strscpy() directly instead.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
[ rjw: Subject and changelog tweaks ]
Link: https://patch.msgid.link/20260112174901.767434-1-thorsten.blum@linux.dev
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>