tools/lib/thermal: Fix include path for libnl3 in pkg-config file.

Fixes pkg-config returning malformed CFLAGS for libthermal.

Signed-off-by: Vibhav Pant <vibhavp@gmail.com>
Link: https://lore.kernel.org/r/20230211081935.62690-1-vibhavp@gmail.com
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>