accel/ivpu: Use struct_size()

Use struct_size() instead of hand-writing it. It is less verbose, more
robust and more informative.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Marco Pagani <marpagan@redhat.com>
Signed-off-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/0ae53be873c27c9a8740c4fe6d8e7cd1b1224994.1685366864.git.christophe.jaillet@wanadoo.fr