app/compress-perf: fix floating point exception

app/compress-perf: fix floating point exception

This patch fixes the floating point exception that happened
when the number of cores to be used during the benchmark
was zero. After the fix such situation is detected, the error
message is printed and the benchmark application exits.

Fixes: 424dd6c8c1a8 ("app/compress-perf: add weak functions for multicore test")
Cc: stable@dpdk.org
Signed-off-by: Adam Dybkowski <adamx.dybkowski@intel.com>
Acked-by: Artur Trybula <arturx.trybula@intel.com>