selftests/bpf: Fix profiler on s390x

Use bpf_probe_read_kernel() and bpf_probe_read_kernel_str() instead
of bpf_probe_read() and bpf_probe_read_kernel().

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/r/20230128000650.1516334-21-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>