iio: adc: ti-ads7950: switch to using guard() notation

iio: adc: ti-ads7950: switch to using guard() notation

guard() notation allows early returns when encountering errors, making
control flow more obvious. Use it.

Reviewed-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Tested-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>