libutils: sp lh comparison w/ pointer

Perhaps the better question is, why have I 100s of times, typed
"ASSERT_NE(nullptr, foo)" for sp<> foo, and got a compiler error and
then change it to "foo.get()". This CL so we can stop wasting cycles
with that error.

Fixes: 147842528
Test: libutils_test
Change-Id: Id63b29d2a1ff3077201a62b69d864c5a826c47e0