fix commit dc9c799c7d vhost: fix missing spinlock unlock
Two regressions were introduced when backporting below
patch:
b4c4e5675c85 ("vhost: fix missing lock protection in power monitor API")

First, rte_vhost_get_monitor_addr did not release the lock
in the success case. Then, rte_rwlock_read_lock() was
converted to rte_spinlock_trylock() instead of
rte_spinlock_lock().

This patch addresses both of these issues.

Fixes: a07736eb68da ("vhost: fix missing lock protection in power monitor API")
Cc: stable@dpdk.org

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>