when enable the multiple workspace, the PLATFORM_DIR still is
$(WORKSPACE)\AnyPkg, even though it is in a PACKAGES_PATH folder. this
patch fix this issue to use the real path.
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>