vfs: make sync_filesystem return errors from ->sync_fs

commit 5679897e upstream.

[backport to 5.10 only differs in __sync_blockdev helper]

Strangely, sync_filesystem ignores the return code from the ->sync_fs
call, which means that syscalls like syncfs(2) never see the error.
This doesn't seem right, so fix that.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>