selftests/bpf: Replace CHECK with ASSERT in test_local_storage

This patch migrates the CHECK macro to ASSERT macro.

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20230308065936.1550103-16-martin.lau@linux.dev


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