Fix v6r8

Typo: item -> items

$ dirac-dms-add-file protonlist.txt
Traceback (most recent call last):
  File "/nfs/magic-ifae01/moralejo/myDIRAC/versions/v0r10p4_1373647582/DIRAC/DataManagementSystem/scripts/dirac-dms-add-file.py", line 60, in <module>
    items[0] = item[0].replace('LFN:','').replace('lfn:','')
NameError: name 'item' is not defined