hwloc: fix condition to display comment message in menuconfig

The comment message shows up if the toolchain has threads instead
of not having threads.

Signed-off-by: Florent Valette <florent.valette@gmail.com>
Reviewed-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>