Three spots call ipa_endpoint_replenish(), and just one of those
requests that the backlog be incremented after completing the
replenish operation.

Instead, have the caller increment the backlog, and get rid of the
add_one argument to ipa_endpoint_replenish().
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>