bus/pci: propagate probing error codes

In a couple of places we check its error code against -EEXIST,
but this function returned either -1, 0, or 1.

This gets critical when hotplugging a device in secondary
process, while the same device is already plugged in the
primary. Failing to "hotplug" it in the primary will cause
the secondary to fail as well.

Fixes: e9d159c3d534 ("eal: allow probing a device again")

Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Acked-by: Thomas Monjalon <thomas@monjalon.net>