drm/i915: Update size upon return from GEM_CREATE

Since GEM_CREATE is trying to outsmart the user by rounding up unaligned
objects, we used to update the size returned to userspace.
This update seems to have been lost throughout the history.

v2: Use round_up(), reorder locals (Chris)

References: ff72145b ("drm: dumb scanout create/mmap for intel/radeon (v3)")
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Janusz Krzysztofik <janusz.krzysztofik@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@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/20190326170218.13255-1-michal.winiarski@intel.com

drivers/gpu/drm/i915/i915_gem.c

@@ -622,14 +622,15 @@ i915_gem_phys_pwrite(struct drm_i915_gem_object *obj,
 static int
 i915_gem_create(struct drm_file *file,
 		struct drm_i915_private *dev_priv,
-		u64 size,
+		u64 *size_p,
 		u32 *handle_p)
 {
 	struct drm_i915_gem_object *obj;
-	int ret;
 	u32 handle;
+	u64 size;
+	int ret;
 
-	size = roundup(size, PAGE_SIZE);
+	size = round_up(*size_p, PAGE_SIZE);
 	if (size == 0)
 		return -EINVAL;
 
@@ -645,6 +646,7 @@ i915_gem_create(struct drm_file *file,
 		return ret;
 
 	*handle_p = handle;
+	*size_p = obj->base.size;
 	return 0;
 }
 
@@ -657,7 +659,7 @@ i915_gem_dumb_create(struct drm_file *file,
 	args->pitch = ALIGN(args->width * DIV_ROUND_UP(args->bpp, 8), 64);
 	args->size = args->pitch * args->height;
 	return i915_gem_create(file, to_i915(dev),
-			       args->size, &args->handle);
+			       &args->size, &args->handle);
 }
 
 static bool gpu_write_needs_clflush(struct drm_i915_gem_object *obj)
@@ -682,7 +684,7 @@ i915_gem_create_ioctl(struct drm_device *dev, void *data,
 	i915_gem_flush_free_objects(dev_priv);
 
 	return i915_gem_create(file, dev_priv,
-			       args->size, &args->handle);
+			       &args->size, &args->handle);
 }
 
 static inline enum fb_op_origin