gbuild: fix rule for gb_ObjCxxObject_get_dep_target
gbuild: fix rule for gb_ObjCxxObject_get_dep_target

The typo causes spurious re-builds and error messages about the
dep-target.

Change-Id: Ia8bc236759c7ef13f81fe91c88f467d6e507bf29

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core