drm/i915: Fix warnings reported by 0-day

Kernel 0-day framework reported warnings with WA batch patches, this patch
fixes those warnings and an additional warning reported in intel_lrc.c file.

Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>