md: dm-req-crypt: Remove few extra checks from write request path

When a request is completed, it frees up req_io to pool. For write
req, it performs few extra checks in a loop. These extra checks are
not required for inline encryption.

Change-Id: I685628bb3be83ec2691db9b1e2147e69a2498b96
Signed-off-by: Dinesh K Garg <dineshg@codeaurora.org>