selftests: bpf: fix backported ASSERT_FALSE

Commit 183d9ebd ("selftests/bpf: Fix core_reloc test runner") causes
builds of selftests/bpf to fail on 5.10.y since the branch doesn't have the
ASSERT_FALSE macro yet. Replace ASSERT_FALSE with ASSERT_EQ.

Fixes: 183d9ebd ("selftests/bpf: Fix core_reloc test runner")
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>