ufs: Use utp_transfer_req_desc pointer in ufshcd_get_tr_ocs

Use utp_transfer_req_desc pointer to reference to utrdl queue
instead of referencing the queue directly. This makes the code
more consistent. No functional change.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Bhupesh Sharma <bhupesh.sharma@linaro.org>
Tested-by: Bhupesh Sharma <bhupesh.sharma@linaro.org>