Use correct stack depot size in __scudo_get_error

This is a no-op but will be used in upcoming scudo changes that allow to
change the depot size at process startup time, and as such we will no
longer be able to call __scudo_get_stack_depot_size in debuggerd.

Bug: 309446692
Change-Id: Ib64b9d042b2a2088484ec5e61944c089a1d85314