block: remove the blk_lookup_devt export

This function is only used by init/do_mounts.c, which can't be modular.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/genhd.c

@@ -1487,7 +1487,6 @@ dev_t blk_lookup_devt(const char *name, int partno)
 	class_dev_iter_exit(&iter);
 	return devt;
 }
-EXPORT_SYMBOL(blk_lookup_devt);
 
 struct gendisk *__alloc_disk_node(int minors, int node_id)
 {