iio: st_sensors: drop ACPI_PTR() and CONFIG_ACPI guards

iio: st_sensors: drop ACPI_PTR() and CONFIG_ACPI guards

The complexity of config guards needed for ACPI_PTR() is not worthwhile
for the small amount of saved data. This example was doing it correctly
but I am proposing dropping this so as to reduce chance of cut and paste
where it is done wrong.  Also drop now unneeded linux/acpi.h include.

Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Denis CIOCCA <denis.ciocca@st.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20231231183514.566609-22-jic23@kernel.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>