Revert unexpected rename in previous patch

Revert unexpected rename in previous patch

While working on the previous patch, I renamed variables whose type I
changed to let the compiler help me find their usages, but I forgot to
rename one back to its original name.  This patch fixes it.

gdb/ChangeLog:

	* varobj.c (struct varobj_dynamic) <children_requested_>: Rename
	back to...
	<children_requested>: ... this.
	(varobj_get_num_children, varobj_update): Adjust.