BaseTools: Fix the bug that incorrect size info in the Lib autogen

The case is a PCD used in one library only, and in DSC component
section the PCD value is override in one of module inf. Then it cause
the bug the PCD size in the Lib autogen use the PCD value in the DSC
PCD section, but not use the override value.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>