drm/i915: Enclose for_each_engine_masked macro arguments in parentheses

Enclose for_each_engine_masked macro arguments in parentheses.

v2:
 * Fixup whitespace to satisfy checkpatch.
 * Likewise reformat to 80 chars.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180406114407.25360-1-tvrtko.ursulin@linux.intel.com