ibmvscsis: Fix the incorrect req_lim_delta

The current code is not correctly calculating the req_lim_delta.

We want to make sure vscsi->credit is always incremented when
we do not send a response for the scsi op. Thus for the case where
there is a successfully aborted task we need to make sure the
vscsi->credit is incremented.

v2 - Moves the original location of the vscsi->credit increment
to a better spot. Since if we increment credit, the next command
we send back will have increased req_lim_delta. But we probably
shouldn't be doing that until the aborted cmd is actually released.
Otherwise the client will think that it can send a new command, and
we could find ourselves short of command elements. Not likely, but could
happen.

This patch depends on both:
commit 25e78531 ("ibmvscsis: Do not send aborted task response")
commit 98883f1b

 ("ibmvscsis: Clear left-over abort_cmd pointers")

Signed-off-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Reviewed-by: Michael Cyr <mikecyr@linux.vnet.ibm.com>
Cc: <stable@vger.kernel.org> # v4.8+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>