test/hash: fix potential memory leak

test/hash: fix potential memory leak

In the multiwriter test, if "found" array allocation failed,
the memory of "keys" array, which was successfully allocated
could not be freed, since by this time, tbl_multiwriter_test_params.keys
was not set to this array, which is the pointer freed when finishing
the test or when a failure happens.

To solve this, tbl_multiwriter_test_params.keys is set to the "keys"
address, just after allocating and filling the array.

Fixes: be856325cba3 ("hash: add scalable multi-writer insertion with Intel TSX")
Cc: stable@dpdk.org
Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>