storaged: Cap io_history when loading stats from disk.

Similar to add_record_locked, load_uid_io_proto should respect the
maximum number of records.

Bug: 111578975
Test: storaged_test.load_uid_io_proto
Change-Id: Ic3c5095cdd09d2184f436813b5ab50d3ee0007b2
Merged-In: Ic3c5095cdd09d2184f436813b5ab50d3ee0007b2