tplist: don't fail if no verbosity is supplied

Initialise the verbosity argument to 0, so that when no verbosity is
provided we don't fail with

$ tplist
kvmmmu:kvm_mmu_pagetable_walk
unorderable types: NoneType() > int()

tools/tplist.py

@@ -26,7 +26,7 @@
  help="List USDT probes in the specified process")
 parser.add_argument("-l", "--lib", default="",
  help="List USDT probes in the specified library or executable")
-parser.add_argument("-v", dest="verbosity", action="count",
+parser.add_argument("-v", dest="verbosity", action="count", default=0,
  help="Increase verbosity level (print variables, arguments, etc.)")
 parser.add_argument(dest="filter", nargs="?",
  help="A filter that specifies which probes/tracepoints to print")