boards: arm: ubx_bmd380eval_nrf52840 - fix doc typo

Corrected reset pin notation from P0.21 to P0.18 in index.rst

Signed-off-by: Bob Recny <[email protected]>

Author: Bob Recny

boards/arm/ubx_bmd380eval_nrf52840/doc/index.rst

@@ -294,7 +294,7 @@ Power (J5)
 +-------+--------------+-------------------------+
 | 2     | VSHLD        | N/A                     |
 +-------+--------------+-------------------------+
-| 3     | RESET        | P0.21 / RESET           |
+| 3     | RESET        | P0.18 / RESET           |
 +-------+--------------+-------------------------+
 | 4     | VSHLD        | N/A                     |
 +-------+--------------+-------------------------+