drm/i915: Handle catastrophic error on engine reset

If cat error is set, we need to clear it by acking it. Further,
if it is set, we must not do a normal request for reset.

v2: avoid goto (Chris)
v3: comment, error format, direct assign (Chris)
Bspec: 12567
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190412165353.16432-1-mika.kuoppala@linux.intel.com