lift the calls of ep_read_events_proc() into the callers

Expand the calls of ep_scan_ready_list() that get ep_read_events_proc().
As a side benefit we can pass depth to ep_read_events_proc() by value
and not by address - the latter used to be forced by the signature
expected from ep_scan_ready_list() callback.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>