block: remove the call to file_remove_privs in blkdev_write_iter

file_remove_privs instantly returns 0 when not called for regular files,
so don't bother.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20230831121911.280155-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>