drm/i915: Improve i915_inject_probe_error macro

drm/i915: Improve i915_inject_probe_error macro

On non-debug builds we were not using i915 param and thus
we may cause "unused variable" warning/error if caller was
not using i915 elsewhere. Let compiler see this param.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
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/20191212121903.72524-1-michal.wajdeczko@intel.com