_eq(), we call get_eqe() before setting eq->nent.  This
is wrong, because get_eqe() uses eq->nent.  Fix this, and clean up the
code a little while we're at it.  (We got lucky with the current code,
because eq->nent was cleared to 0, which get_eqe() made happen to do
the right thing)

Pointed out by Michael S. Tsirkin <mst@mellanox.co.il>

Signed-off-by: Roland Dreier <rolandd@cisco.com>
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