PM: hibernate: 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.

This kernel config option is simply assigned with the resume_file
buffer. It should be NUL-terminated but not necessarily NUL-padded as
per its further usage with other string apis:
|	static int __init find_resume_device(void)
|	{
|		if (!strlen(resume_file))
|			return -ENOENT;
|
|		pm_pr_dbg("Checking hibernation image partition %s\n", resume_file);

Use strscpy() [2] as it guarantees NUL-termination on the destination
buffer. Specifically, use the new 2-argument version of strscpy()
introduced in Commit e6584c3964 ("string: Allow 2-argument
strscpy()").

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: Kees Cook <keescook@chromium.org>
Reviewed-by: Dhruva Gole <d-gole@ti.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

kernel/power/hibernate.c

@@ -1361,7 +1361,7 @@ static int __init resume_setup(char *str)
 	if (noresume)
 		return 1;
 
-	strncpy(resume_file, str, 255);
+	strscpy(resume_file, str);
 	return 1;
 }