clockintr: rename "struct clockintr_queue" to "struct clockqueue"

clockintr: rename "struct clockintr_queue" to "struct clockqueue"

The code has outgrown the original name for this struct.  Both the
external and internal APIs have used the "clockqueue" namespace for
some time when operating on it, and that name is eyeball-consistent
with "clockintr" and "clockrequest", so "clockqueue" it is.