block: don't call invalidate_partition from blk_drop_partitions

Given that the device must not be busy, most of the calls from
invalidate_partition that are related to file system metadata are
guranteed to not happen.  Just open code the calls to sync_blockdev
and invalidate_bdev instead.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/partitions/core.c

@@ -607,15 +607,14 @@ int blk_drop_partitions(struct block_device *bdev)
 {
 	struct disk_part_iter piter;
 	struct hd_struct *part;
-	int res;
 
 	if (!disk_part_scan_enabled(bdev->bd_disk))
 		return 0;
 	if (bdev->bd_part_count || bdev->bd_openers > 1)
 		return -EBUSY;
-	res = invalidate_partition(bdev->bd_disk, 0);
-	if (res)
-		return res;
+
+	sync_blockdev(bdev);
+	invalidate_bdev(bdev);
 
 	disk_part_iter_init(&piter, bdev->bd_disk, DISK_PITER_INCL_EMPTY);
 	while ((part = disk_part_iter_next(&piter)))