drm/panthor: Fix wrong kernel-doc format in the uAPI header

The kernel doc prefix is /** not /*.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240326093055.411932-1-boris.brezillon@collabora.com