iio: fix pointer cast warning

fix compile warning reported by Fengguang Wu:

drivers/iio/light/adjd_s311.c: In function 'adjd_s311_trigger_handler':
drivers/iio/light/adjd_s311.c:188:12: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
drivers/iio/light/adjd_s311.c:188:4: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]

   185              }
   186
   187              if (indio_dev->scan_timestamp)
 > 188                      *(s64 *)((phys_addr_t)data->buffer + ALIGN(len, sizeof(s64)))
   189                              = time_ns;
   190              iio_push_to_buffer(buffer, (u8 *)data->buffer, time_ns);
   191

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>