selftests/bpf: Use producer_cnt to allocate local counter array

For count-local benchmark, use producer_cnt instead of consumer_cnt when
allocating local counter array.

Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20230613080921.1623219-2-houtao@huaweicloud.com


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