test/hash: rectify slave id to point to valid cores

test/hash: rectify slave id to point to valid cores

This patch rectifies slave_id to point to valid core indexes rather than
core ranks in read-write lock-free concurrency test.

It also replaces a 'for' loop with RTE_LCORE_FOREACH API.

Fixes: c7eb0972e74b ("test/hash: add lock-free r/w concurrency")
Cc: stable@dpdk.org
Signed-off-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Yipeng Wang <yipeng1.wang@intel.com>