eal: fix multi-process hotplug if attached in secondary

eal: fix multi-process hotplug if attached in secondary

Consider the following scenario:

 1) primary process (A) starts, probes the bus
 2) a secondary process (B) starts, probes the bus
 3) yet another secondary process (C) starts
 4) (C) registers the pci driver and hotplugs the device
    * an IPC attach req is sent to the primary (A)
      * (A) ignores the -EEXIST from process-local probe
      * (A) propagates the request to all secondary processes
        * (B) responds with -EEXIST
      * (A) replies to the original request with the -EEXIST
        return code
    * the -EEXIST is returned back to the user, although the
      device was successfully attached both locally and in
      all other processes

This patch makes the primary process reply with rc=0 even if
there was another secondary process with the device already
attached. The primary process already didn't reply with -EEXIST
when the device was attached locally, so now this behavior is
even more consistent. Looking by the code, this seems to be the
originally intended behavior.

Fixes: ac9e4a17370f ("eal: support attach/detach shared device from secondary")

Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Acked-by: Qi Zhang <qi.z.zhang@intel.com>