ib_acme: Better error handling in resolve_gid

A return of 0 is an error for inet_pton but if 0 is returned
from resolve_gid, show_path is mistakenly called so if
0 is returned from inet_pton, return -1 instead (which is
what is done elsewhere in acme).

Signed-off-by: Hal Rosenstock <hal@mellanox.com>
Signed-off-by: Sean Hefty <sean.hefty@intel.com>