Commit 5149e343 removed the return value of getconfig_dir() when
compiling for OSX.

Change-Id: I1d3729083adfb487f7b7cf2f0e8ee3a1a56e1192
Tested-by: Alexandre Lision <alexandre.lision@savoirfairelinux.com>
Reviewed-by: Guillaume Roguez <guillaume.roguez@savoirfairelinux.com>