drm/xe/display: use correct bo type in intel_fbdev_fb_alloc()

drm/xe/display: use correct bo type in intel_fbdev_fb_alloc()

It's really struct xe_bo, and struct drm_i915_gem_object only works
because of -Ddrm_i915_gem_object=xe_bo in xe Makefile.

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/344a5a4c88a3ce17dd276b0155bcdbf93e5fb475.1726589119.git.jani.nikula@intel.com