MdePkg: Correct the string expression of UTF8 vendor device path

MdePkg: Correct the string expression of UTF8 vendor device path

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
display it as: VenUft8() by mistake when convert device
path node to text.

This commit is to fix this bug.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>