deploy: Avoid trying to change immutable state unnecessarily

deploy: Avoid trying to change immutable state unnecessarily

For some reason I haven't fully debugged (probably a recent
kernel change), in the case where the immutable bit isn't set,
trying to call `EXT2_IOC_SETFLAGS` without it set returns `EINVAL`.

Let's avoid calling the `ioctl()` if we don't have anything to do.

This fixes a slew of `make check` failures here in my toolbox
environment.

(kernel is `5.5.0-0.rc6.git0.1.fc32.x86_64` with `xfs`)