sstatesig: Ensure we return all matches for find_sigdata

sstatesig: Ensure we return all matches for find_sigdata

When the hashes to find isn't specified we need to return matches from both
the sstate cache and the local stamps directory regardless of how many we've
found so far. If we don't do this, we can miss stamps and the comparison is
less accurate/incorrect.

(From OE-Core rev: 08a074e11e2d517b81ca71fd9bda65297bb015a7)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>