test: proceed if timer subsystem already initialized

test: proceed if timer subsystem already initialized

rte_timer_subsystem_init() may return -EALREADY if the timer subsystem
was already initialized. This can happen i.e. in PMD code (see
eth_ena_dev_init). This is not an error, rather a notification as the
initialization function simply returns without any action taken.

Fixes: 50247fe03fe0 ("test/timer: exercise new APIs in secondary process")
Cc: stable@dpdk.org
Signed-off-by: Stanislaw Kardach <kda@semihalf.com>
Reviewed-by: Michal Krawczyk <mk@semihalf.com>