drm/i915/buddy: add missing call to i915_global_register

We are meant to register the kmem cache at init, such the supplied exit
and shrink hooks can be called.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190905072921.7979-1-matthew.auld@intel.com

drivers/gpu/drm/i915/i915_buddy.c

@@ -38,6 +38,7 @@ int __init i915_global_buddy_init(void)
 	if (!global.slab_blocks)
 		return -ENOMEM;
 
+	i915_global_register(&global.base);
 	return 0;
 }