BaseTools/UPT: Update the import statement to use StringUtils

The patch 5a57246eab Rename String to StringUtils, but it didn't
update the UPT Tool for the import statement which cause UPT tool
break.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

BaseTools/Source/Python/UPT/Library/UniClassObject.py

@@ -23,7 +23,7 @@ import distutils.util
 from Logger import ToolError
 from Logger import Log as EdkLogger
 from Logger import StringTable as ST
-from Library.String import GetLineNo
+from Library.StringUtils import GetLineNo
 from Library.Misc import PathClass
 from Library.Misc import GetCharIndexOutStr
 from Library import DataType as DT