ice(4): Stop checking for failures from malloc(M_WAITOK)

As a consequence now ice_alloc_vsi_qmap() does not fail. Remove unneeded
error checks.

MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D45852

(cherry picked from commit 5f97656fa334b494d70866cb1bfff406d3efd92d)
(cherry picked from commit bb8c6f43256d234d492c267d74526fc62102b23d)