drm/i915: use pointer = k[cmz...]alloc(sizeof(*pointer), ...) pattern

Done while reviewing all our allocations for fubar. Also a few errant
cases of lacking () for the sizeof operator - just a bit of OCD.

I've left out all the conversions that also should use kcalloc from
this patch  (it's only 2).

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 36c4ad9..96f65a1 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4638,7 +4638,7 @@
 	if (dev_priv->mm.phys_objs[id - 1] || !size)
 		return 0;
 
-	phys_obj = kzalloc(sizeof(struct drm_i915_gem_phys_object), GFP_KERNEL);
+	phys_obj = kzalloc(sizeof(*phys_obj), GFP_KERNEL);
 	if (!phys_obj)
 		return -ENOMEM;