drm/xe/device: fix XE_MAX_TILES_PER_DEVICE check

Here XE_MAX_TILES_PER_DEVICE is the gt array size, therefore the gt
index should always be less than.

v2 (Lucas):
  - Add fixes tag.

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>
Acked-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240318180532.57522-6-matthew.auld@intel.com