prov/psm: fix the return value of fi_av_insert

The function should return the number of addresses resolved.
Addresses that have failed to resolve are indicated by the value
FI_ADDR_NOTAVAIL in the result fi_addr array. Negative error code
is returned when errors other than "failed address resolution"
have happened.

This fixes bug #413.

Signed-off-by: Jianxin Xiong <jianxin.xiong@intel.com>