ravenscar: update inferior ptid with event ptid

ravenscar: update inferior ptid with event ptid

When debugging a program using a ravenscar runtime, the thread
layer sometimes gets confused, and even missing some threads.
This was traced to an assumption that ravenscar_wait was making,
which is that calling the "to_wait" target_ops method would
set the inferior_ptid, so that we could then use that assumption
to update our thread_list and current ptid. However, this has not
been the case for quite a while now. This patch fixes the problem
by assigning inferior_ptid the ptid returned by "to_wait".

gdb/ChangeLog:

	* ravenscar-thread.c (ravenscar_wait): Update inferior ptid
	with event ptid from the lower layer before doing the
	ravenscar-specific update.