eal: fix build with gcc 9.0

eal: fix build with gcc 9.0

build error:
In function ‘eal_plugin_add’,
    .../lib/librte_eal/common/eal_common_options.c:225:2:
    error: ‘strncpy’ output may be truncated copying 4095 bytes from a
           string of length 4095 [-Werror=stringop-truncation]
    strncpy(solib->name, path, PATH_MAX-1);

strncpy may result a not null-terminated string,
replaced it with strlcpy

Fixes: f9a08f650211 ("eal: add support for shared object drivers")
Cc: stable@dpdk.org
Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>