abandon: fix usage of undefined variable

As reported by pyflakes:

  subcmds/abandon.py:84: undefined name 'p'

The name of the variable should be 'proj'.

Change-Id: Ic09eb92e8db6b510e99efce010bd0bb094d7cbfe

subcmds/abandon.py

@@ -81,7 +81,7 @@ It is equivalent to "git branch -D <branchname>".
         err_msg = "error: cannot abandon %s" %br
         print(err_msg, file=sys.stderr)
         for proj in err[br]:
-          print(' '*len(err_msg) + " | %s" % p.relpath, file=sys.stderr)
+          print(' '*len(err_msg) + " | %s" % proj.relpath, file=sys.stderr)
       sys.exit(1)
     elif not success:
       print('error: no project has local branch(es) : %s' % nb,