eal/linux: fix memory leak in uevent handling

eal/linux: fix memory leak in uevent handling

When the memory for uevent.devname is allocated in dev_uev_parse(). It
is not freed when parse the subsystem layer fails in dev_uev_parse().
Before return, it is also not freed in dev_uev_handler(). These cause a
memory leak.

Fixes: 0d0f478d0483 ("eal/linux: add uevent parse and process")
Cc: stable@dpdk.org
Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>