kvm/vfio: Fix potential deadlock problem in vfio

Fix following coccicheck warning:
./virt/kvm/vfio.c:258:1-7: preceding lock on line 236

If kvm_vfio_file_iommu_group() failed, code would goto err_fdput with
mutex_lock acquired and then return ret. It might cause potential
deadlock. Move mutex_unlock bellow err_fdput tag to fix it.

Fixes: d55d9e7 ("kvm/vfio: Store the struct file in the kvm_vfio_group")
Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20220517023441.4258-1-wanjiabing@vivo.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

virt/kvm/vfio.c

@@ -252,8 +252,8 @@ static int kvm_vfio_group_set_spapr_tce(struct kvm_device *dev,
 		break;
 	}
 
-	mutex_unlock(&kv->lock);
 err_fdput:
+	mutex_unlock(&kv->lock);
 	fdput(f);
 	return ret;
 }