BaseTools:fix Ecc tool issue for check StructPcd

BaseTools:fix Ecc tool issue for check StructPcd

BZ:https://bugzilla.tianocore.org/show_bug.cgi?id=2142

gAdvancedFeaturePkgTokenSpaceGuid.PcdSmbiosType0BiosInformation|
{0x0}|SMBIOS_TABLE_TYPE0|0x80010000 {
    <HeaderFiles>
      IndustryStandard/SmBios.h
    <Packages>
      MdePkg/MdePkg.dec
      AdvancedFeaturePkg/AdvancedFeaturePkg.dec
  }

If there's a PcdStructHF or PcdStructPKGs in StructPcd,
EccTool report error,IndexError: list index out of range

This patch is going to fix this issue

Cc: Liming Gao <liming.gao@intel.com>
Cc: Bob Feng <bob.c.feng@intel.com>
Signed-off-by: Zhiju.Fan <zhijux.fan@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>