Fix several bugs in the implementation of converting SAS/SASEX device path node from/to text.

Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@14256 6f19259b-4bc3-4df7-8a09-765794883524