IB/qib: Remove empty function

Commit f0626710

 ("RDMA: Update workqueue usage") removed
content of qib_qsfp_deinit(...) and left it empty.

This patch deletes all leftovers of that function.

Signed-off-by: Leon Romanovsky <leon@kernel.org>
Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>