FAT: use io_schedule_timeout() instead of congestion_wait()

congestion_wait() in this context is just a sleep - block devices do not
support congestion signalling any more.

The goal for this wait, which was introduced in commit ae78bf9c
("[PATCH] add -o flush for fat") is to wait for any recently written
data to get to storage.  We currently have no direct mechanism to do
this, so a simple wait that behaves identically to the current
congestion_wait() is the best we can do.

This is a step towards removing congestion_wait()

Link: https://lkml.kernel.org/r/163936544519.22433.13400436295732112065@noble.neil.brown.nameSigned-off-by: NeilBrown <neilb@suse.de>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/fat/file.c

@@ -177,7 +177,8 @@ static int fat_file_release(struct inode *inode, struct file *filp)
 	if ((filp->f_mode & FMODE_WRITE) &&
 	    MSDOS_SB(inode->i_sb)->options.flush) {
 		fat_flush_inodes(inode->i_sb, inode, NULL);
-		congestion_wait(BLK_RW_ASYNC, HZ/10);
+		set_current_state(TASK_UNINTERRUPTIBLE);
+		io_schedule_timeout(HZ/10);
 	}
 	return 0;
 }