nvme_rdma_pre_copy_mem() does not have any failure cases, so remove its
return value and remove the never-taken branch in its only caller,
nvme_rdma_qpair_submit_request().
Change-Id: I91011734ed0c20f8db691d62172fe1a3021dd3a1
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>