eal: fix errno on service cores init failure

eal: fix errno on service cores init failure

Currently, when rte_service_init() fails at initialization, we
see the following message:

  Cannot init EAL: Exec format error

This error code does describe the real issue. Instead, use the error
code returned by the function.

Fixes: e39824500825 ("service: initialize with EAL")
Cc: stable@dpdk.org
Signed-off-by: Olivier Matz <olivier.matz@6wind.com>