iio:adc:sd_adc_modulator: Drop of_match_ptr and tweak includes

Dropping of_match_ptr allows this driver to be used with ACPI.
The header includes are adjusted to include platform_device.h
and mod_devicetable.h instead of OF specific header as nothing
from that header itself is actually used.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>