Revert "RDMA/usnic: use iommu_map_atomic() under spin_lock()"

This reverts commit 80282a3d which is
commit b7e08a5a63a11627601915473c3b569c1f6c6c06 upstream.

It will not build as a pre-requsite commit was reverted as it broke the
Android kernel abi and it was needed for this change.  This change is
not needed for Android systems so it is safe to revert.

Bug: 161946584
Change-Id: I4dabb4a6943fc128fb54c8f7a80a694823c1c5f8
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>