hw/s390x/ccw-device: Fix memory leak in loadparm setter

hw/s390x/ccw-device: Fix memory leak in loadparm setter

Commit bdf12f2a fixed the setter for the "loadparm" machine property,
which gets a string from a visitor, passes it to s390_ipl_fmt_loadparm()
and then forgot to free it. It left another instance of the same problem
unfixed in the "loadparm" device property. Fix it.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20250625082751.24896-1-kwolf@redhat.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Tested-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>