block: unexport disk_get_part

disk_get_part is not used by any modular code.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/genhd.c

@@ -217,7 +217,6 @@ struct hd_struct *disk_get_part(struct gendisk *disk, int partno)
 
 	return part;
 }
-EXPORT_SYMBOL_GPL(disk_get_part);
 
 /**
  * disk_part_iter_init - initialize partition iterator