s390/vfio-ap: fix an error handling path in vfio_ap_mdev_probe_queue()

s390/vfio-ap: fix an error handling path in vfio_ap_mdev_probe_queue()

The commit in Fixes: has switch the order of a sysfs_create_group() and a
kzalloc().

It correctly removed the now useless kfree() but forgot to add a
sysfs_remove_group() in case of (unlikely) memory allocation failure.

Add it now.

Fixes: 260f3ea14138 ("s390/vfio-ap: move probe and remove callbacks to vfio_ap_ops.c")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Link: https://lore.kernel.org/r/d0c0a35eec4fa87cb7f3910d8ac4dc0f7dc9008a.1659283738.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>