hwloc-bind: fix an uninitialized warning

pid is only used when pid_number > 0 but gcc-4.8 doesn't seem
to understand that.

(cherry picked from commit a3c5dfee923fa305ba191eeda25122ddaeeb39a4)
hwloc-calc.h: fix some (useless) warning about data being used without being initialized

(cherry picked from commit abee2413e0366a8d57f6cc702d47264e6e590c3b)