drm/nouveau: exec: fix ioctl kernel-doc warning

kernel-doc emits a warning:

include/uapi/drm/nouveau_drm.h:49: warning: Cannot understand  * @NOUVEAU_GETPARAM_EXEC_PUSH_MAX
 on line 49 - I thought it was a doc line

We don't have a way to document a macro value via kernel-doc, so
change the "/**" kernel-doc marker to a C comment and format the comment
more like a kernel-doc comment for consistency.

Fixes: d59e75ee ("drm/nouveau: exec: report max pushs through getparam")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Danilo Krummrich <dakr@redhat.com>
Cc: Karol Herbst <kherbst@redhat.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Cc: nouveau@lists.freedesktop.org
Cc: Bragatheswaran Manickavel <bragathemanick0908@gmail.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231008140231.17921-1-rdunlap@infradead.org