IB/core: fix null pointer deref and mem leak in error handling

The current error handling in setup_hw_stats has a couple of issues.
It is possible to generate a null pointer deference on the
kfree of hsag->attrs[i] because two of the early error exit paths
jump to the kfree when hsags NULL and not allocated. Fix this by
moving the kfree on stats and jumping to that, avoiding the hsag
freeing.

Secondly, there is a memory leak of stats if the hsag allocation
fails; instead of returning, jump to the kfree on stats.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>