iio: sx9324: Fix register field spelling

Field for PROX_CTRL4 should contain PROX_CTRL4.

Fixes: 4c18a890 ("iio:proximity:sx9324: Add SX9324 support")
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20220429220144.1476049-3-gwendal@chromium.org


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>