cxgb: several issues

[Maxime Villard <max%m00nbsd.net@localhost>]

Mootja tells me that there is a memory leak here [1]. 'm' is allocated and
overwritten at l.130. The problem is, it seems to me 'm' is actually useless,
but I'm not sure if it somehow gets referenced earlier. Note, by the way, that
there is a similar bug later: at l.162 'm0' is allocated, and then overwritten
at l.185. And again, I'm not sure whether the leak can be triggered or not.

Does someone have an idea? If not, I guess I'll just add some XXXs and file a
PR.

[1] https://nxr.netbsd.org/xref/src/sys/dev/pci/cxgb/cxgb_l2t.c#106