Replace strcpy() with strscpy() in the ACPI backlight code.

strcpy() has been deprecated because it is generally unsafe, so help to
eliminate if from the kernel source.

Link: https://github.com/KSPP/linux/issues/88Signed-off-by: Muhammad Qasim Abdul Majeed <qasim.majeed20@gmail.com>
Link: https://patch.msgid.link/20240703084124.11530-1-qasim.majeed20@gmail.com
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>