growfs: Expand FS even if underlying block expansion fails

growfs: Expand FS even if underlying block expansion fails

This allows growfs to expand the filesystem even when the underlying
block device cannot be expanded. This has been useful for example on
LUKS devices that have already been expanded using systemd-repart.

This works around the following error:
```
root@mobian:/home/mobian# /usr/lib/systemd/systemd-growfs /
crypt_resize() of /dev/block/179:2 failed: Operation not permitted
```