libefivar: Correct the string expression of UTF8 vendor device path

[jlduran_gmail.com]

Summary

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1225

According to UEFI spec, the string expression of UTF8 vendor device node should be displayed as: VenUtf8(). Current code displays it as: VenUft8() by mistake when converting device path node to text.

This commit fixes this bug.

Obtained from: https://github.com/tianocore/edk2/commit/959be180e185869b71db9dad34c3f4bba660d724

[jlduran_gmail.com]

Moving this, formerly GitHub PR #580, here.

[jlduran_gmail.com]

Landed as 91a35e5803bef59b8ca67b0621216124cc2e42f8.