[gdb/python] Fix cpychecker error in pspy_solib_name

When using cpychecker, we run into:
...
gdb/python/py-progspace.c: \
  In function ‘PyObject* pspy_solib_name(PyObject*, PyObject*)’:
gdb/python/py-progspace.c:370:25: error: Mismatching type in call to \
  PyArg_ParseTuple with format code "K" [-Werror]
   if (!PyArg_ParseTuple (args, GDB_PY_LLU_ARG, &pc))
  argument 3 ("&pc") had type
    "gdb_py_longest *" (pointing to 64 bits)
  but was expecting
    "long long unsigned int *" (pointing to 64 bits)
  for format code "K"
...

Fix this fixing the type of the variable.

Build and reg-tested on x86_64-linux.

2018-10-05  Tom de Vries  <tdevries@suse.de>

	* python/py-progspace.c (pspy_solib_name): Fix type mismatch in
	PyArg_ParseTuple call.

gdb/python/py-progspace.c

@@ -362,7 +362,7 @@ static PyObject *
 pspy_solib_name (PyObject *o, PyObject *args)
 {
   char *soname;
-  gdb_py_longest pc;
+  gdb_py_ulongest pc;
   pspace_object *self = (pspace_object *) o;
 
   PSPY_REQUIRE_VALID (self);