i915: fix vbl swap allocation size.

This is upstream as 54583bf4

Oops...
Signed-off-by: Dave Airlie <airlied@linux.ie>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/char/drm/i915_irq.c

@@ -541,7 +541,7 @@ int i915_vblank_swap(DRM_IOCTL_ARGS)
 		return DRM_ERR(EBUSY);
 	}
 
-	vbl_swap = drm_calloc(1, sizeof(vbl_swap), DRM_MEM_DRIVER);
+	vbl_swap = drm_calloc(1, sizeof(*vbl_swap), DRM_MEM_DRIVER);
 
 	if (!vbl_swap) {
 		DRM_ERROR("Failed to allocate memory to queue swap\n");