btrfs: fix EIO misuse to report missing degraded option

EIO is only for the IO failure to the device, avoid it. Use ENOENT as
that's the closest error code describing what happened.
Signed-off-by: NAnand Jain <anand.jain@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
[ update changelog ]
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -6437,7 +6437,7 @@ static int read_one_chunk(struct btrfs_fs_info *fs_info, struct btrfs_key *key,
 		    !btrfs_test_opt(fs_info, DEGRADED)) {
 			free_extent_map(em);
 			btrfs_report_missing_device(fs_info, devid, uuid);
-			return -EIO;
+			return -ENOENT;
 		}
 		if (!map->stripes[i].dev) {
 			map->stripes[i].dev =
@@ -6570,7 +6570,7 @@ static int read_one_dev(struct btrfs_fs_info *fs_info,
 	if (!device) {
 		if (!btrfs_test_opt(fs_info, DEGRADED)) {
 			btrfs_report_missing_device(fs_info, devid, dev_uuid);
-			return -EIO;
+			return -ENOENT;
 		}
 
 		device = add_missing_dev(fs_devices, devid, dev_uuid);
@@ -6585,7 +6585,7 @@ static int read_one_dev(struct btrfs_fs_info *fs_info,
 		if (!device->bdev) {
 			btrfs_report_missing_device(fs_info, devid, dev_uuid);
 			if (!btrfs_test_opt(fs_info, DEGRADED))
-				return -EIO;
+				return -ENOENT;
 		}
 
 		if(!device->bdev && !device->missing) {