gdbserver/event-loop.c: type mismatch

gdbserver/event-loop.c: type mismatch

Building with C++ catches a buglet here:

../../../src/gdb/gdbserver/event-loop.c:205:19: warning: invalid conversion from ‘gdb_client_data {aka void*}’ to ‘void**’ [-fpermissive]
   event_ptr->data = data;
                   ^

This works in practice because gdb_client_data is a pointer already
(hence in C we get an implicit conversion), and nothing deferences the
pointer.  It's passed from client at event registration/creation time,
only to pass straight back to client callback.

Well, that and nothing in gdbserver uses the event data anyway.

gdb/gdbserver/ChangeLog:
2015-07-10  Pedro Alves  <palves@redhat.com>

	* event-loop.c (struct callback_event) <data>: Change type to
	gdb_client_data instance instead of gdb_client_data pointer.
	(append_callback_event): Adjust.