boards: hardkernel: odroid_go: fix PSRAM size

Booting the hello world sample fails with an error on the odroid go:

  I (124) quad_psram: This chip is ESP32-D0WD
  I (124) esp_psram: Found 4MB PSRAM device
  I (124) esp_psram: Speed: 40MHz
  I (125) esp_psram: PSRAM initialized, cache is in normal (1-core) mode.
  SPIRAM size is less than configured size, aborting.
  abort()

The device features only 32 Mbit PSRAM (4 MiB), see

  dts/xtensa/espressif/esp32/esp32_wrover_e_n16r4.dtsi

included from

  boards/hardkernel/odroid_go/odroid_go_procpu.dts

Signed-off-by: Gero Schwäricke <gero.schwaericke@posteo.de>