Fix error when using -p

args.file is never set after Ieb9a87f16cf5e1c07a65186eff5df26d4ffcdd33,
add a helper function to get the file instead to fix:
Traceback (most recent call last):
  File "./update_current.py", line 576, in <module>
    if args.file:
AttributeError: 'Namespace' object has no attribute 'file'

Test: ./update_current.py -p 4583087
Change-Id: I4fdcf76a267e70f3eb3f3ec8a641983fd91b8357
1 file changed