iio: proximity: sx_common: Drop documentation of non existent struct element.

struct sx_common_data doesn't have a num_default_regs element so
drop the documentation for it.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Gwendal Grignou <gwendal@chromium.org>
Cc: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20230114172928.80414-1-jic23@kernel.org


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