Here I've kept the selection of IIO_SW_RING separate from
IIO_TRIGGER as it will go away fairly shortly when the ring buffer
type becomes configurable on a per device basis, whereas the
IIO_TRIGGER select will remain. Whether to retain the option to
remove the support for ring buffers entirely is one for after that
support is in place.

Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>