selftests/bpf: Fix result check for test_bpf_hash_map

The original condition looks like a typo, verify the skeleton loading
result instead.

Signed-off-by: Dmitrii Dolgov <9erthalion6@gmail.com>
Link: https://lore.kernel.org/r/20220510155233.9815-3-9erthalion6@gmail.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>