Check return value bounds: update test

[kkjeer]

This PR updates the hash.c test file to account for the compiler behavior in checkedc-clang/1150: checking that the inferred bounds of a return expression imply the declared bounds (if any) for the enclosing function.

There was one function localmalloc in hash.c that returned a variable blah with unknown bounds, which resulted in a compile-time error. This PR declares the bounds byte_count(size) for blah to match the declared bounds byte_count(size) of the localmalloc function.

[sulekhark]

LGTM! Thanks!