drm/xe/queue: fix engine_class bounds check

The engine_class is the index into the user_to_xe_engine_class,
therefore it needs to be less than.

Fixes: dd08ebf6

 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240318180532.57522-4-matthew.auld@intel.com