ufs: Fix usage of WARN_ON()

WARN_ON() was being incorrectly called without a condition in
ufsdbg_intr_fail_request().

Fixes: 2d8e79c2 ("ufs: Porting UFS driver's changes from kernel msm-4.14 to msm-kona")
Change-Id: Ic0dedbad345f74f1686c29e3e4c775737bebb231
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>