iio: sw-trigger: Fix config group initialization

Use the IS_ENABLED() helper macro to ensure that the configfs group is
initialized either when configfs is built-in or when configfs is built as a
module. Otherwise software trigger creation will result in undefined
behaviour when configfs is built as a mdoule since the configfs group for
the trigger is not properly initialized.

Fixes: b662f809 ("iio: core: Introduce IIO software triggers")
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Daniel Baluta <daniel.baluta@intel.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

include/linux/iio/sw_trigger.h

@@ -62,7 +62,7 @@ void iio_swt_group_init_type_name(struct iio_sw_trigger *t,
 				  const char *name,
 				  struct config_item_type *type)
 {
-#ifdef CONFIG_CONFIGFS_FS
+#if IS_ENABLED(CONFIG_CONFIGFS_FS)
 	config_group_init_type_name(&t->group, name, type);
 #endif
 }