drm/i915/gvt: Use ARRAY_SIZE for vgpu_types

Prefer ARRAY_SIZE instead of using sizeof

Fixes coccicheck warning: Use ARRAY_SIZE

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Aishwarya Ramakrishnan <aishwaryarj100@gmail.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200518150336.15265-1-aishwaryarj100@gmail.com