iio: sca3000: manage device registration with devm helper

iio: sca3000: manage device registration with devm helper

Convert the iio registration to use devm_* helpers so the probe no
longer needs a separate cleanup path and remove callback can also drop
the unregister. After this there is no need for having a remove
callback, so remote it.

No functional change intended.

Suggested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Reviewed-by: David Lechner <dlechner@baylibe.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>