vfio: More vfio_file_is_group() use cases

Replace further open coded tests with helper.
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/166516896843.1215571.5378890510536477434.stgit@omenSigned-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/vfio_main.c

@@ -1615,7 +1615,7 @@ bool vfio_file_enforced_coherent(struct file *file)
 	struct vfio_group *group = file->private_data;
 	bool ret;
 
-	if (file->f_op != &vfio_group_fops)
+	if (!vfio_file_is_group(file))
 		return true;
 
 	mutex_lock(&group->group_lock);
@@ -1647,7 +1647,7 @@ void vfio_file_set_kvm(struct file *file, struct kvm *kvm)
 {
 	struct vfio_group *group = file->private_data;
 
-	if (file->f_op != &vfio_group_fops)
+	if (!vfio_file_is_group(file))
 		return;
 
 	mutex_lock(&group->group_lock);
@@ -1667,7 +1667,7 @@ bool vfio_file_has_dev(struct file *file, struct vfio_device *device)
 {
 	struct vfio_group *group = file->private_data;
 
-	if (file->f_op != &vfio_group_fops)
+	if (!vfio_file_is_group(file))
 		return false;
 
 	return group == device->group;