`spd` no longer prints usefully on gimlets

[rmustacc]

In the past humility spd gave useful output on a gimlet. Now we're getting the raw array contents dumped to us:

rm@cadbury ~ $ ./humility --version
humility 0.12.12 
rm@cadbury ~ $ pfexec ./humility -t c71 spd
humility: attached to 0483:3754:001100184741500820383733 via ST-Link V3
humility spd failed: not an array: Struct(Struct { name: "SpdData<16, 512>", members: {"spd_present": Array(Array([Base(Bool(true)), Base(Bool(true)), Base(Bool(true)), Base(Bool(true)), Base(Bool(true)), Base(Bool(true)), Base(Bool(true)), Base(Bool(true)), Base(Bool(true)), Base(Bool(true)), Base(Bool(true)), Base(Bool(true)), Base(Bool(true)), Base(Bool(true)), Base(Bool(true)), Base(Bool(true))])), "spd_data": Array(Array([Array(Array([Base(U8(35)), Base(U8(20)), Base(U8(12)), Base(U8(1)), Base(U8(134)), Base(U8(49)), Base(U8(0)), Base(U8(8)), Base(U8(0)), Base(U8(112)), Base(U8(0)), Base(U8(3)), Base(U8(8)), Base(U8(11)), Base(U8(128)), Base(U8(0)), Base(U8(0)), Base(U8(0)), Base(U8(5)), Base(U8(13)), Base(U8(248)), Base(U8(255)), Base(U8(2)), Base(U8(0)), Base(U8(110)), Base(U8(110)), Base(U8(110)), Base(U8(17)), Base(U8(0)), Base(U8(110)), Base(U8(240)), Base(U8(10)), Base(U8(32)), Base(U8(8)),
...
rm@cadbury ~ $ echo $?
1