Correct type/array element offset in LibraryCallKit::get_state_from_digest_object()

In LibraryCallKit::get_state_from_digest_object() we call array_element_address() with T_INT, even though the input array might also be T_BYTE or T_LONG. This doesn't currently matter much: array elements always start at the same offset regardless of the element type. In Lilliput I'm trying to tighten the start of array elements though, and this causes problems because I can do smaller alignments for T_BYTE and T_INT, but not for T_LONG.

See also: https://github.com/openjdk/lilliput/pull/41

Let's just use the correct type in array_element_address().