boards: nordic_nrf: fix broken references

Those were likely updated by mistake when changing to HWMv2.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>

boards/nordic_nrf/nrf52840dk/doc/index.rst

@@ -222,7 +222,7 @@ Overview
 ********
 
 The nrf52840dk/nrf52811 board variant is a modified version of the
-:ref:`nrf52840dk/nrf52840` that enforces the limitations imposed by the nRF52811
+:ref:`nrf52840dk_nrf52840` that enforces the limitations imposed by the nRF52811
 IC, which is a variant of the original nRF52840. Since Nordic does not offer a
 development kit for the nRF52811 you can use this board to develop for this IC
 while using the nRF52840 Development Kit (PCA10056).

boards/nordic_nrf/nrf9160dk/doc/index.rst

@@ -105,7 +105,7 @@ should be used when building your application (for more information, see
    :compact:
 
 Remember to also enable routing for this additional hardware in the firmware for
-:ref:`nrf9160dk/nrf52840` (see :ref:`nrf9160dk_board_controller_firmware`).
+:ref:`nrf9160dk_nrf52840` (see :ref:`nrf9160dk_board_controller_firmware`).
 
 Other hardware features have not been enabled yet for this board.
 See `nRF9160 DK website`_ and `Nordic Semiconductor Infocenter`_