boards: efm32pg_stk3402a: Update outdated schematic link

This commit updates the outdated schematic link for the board.

Signed-off-by: Stephanos Ioannidis <[email protected]>

Author: stephanosio

boards/arm/efm32pg_stk3402a/doc/index.rst

@@ -197,7 +197,7 @@ terminal session:
    https://www.silabs.com/documents/public/user-guides/ug257-stk3402-usersguide.pdf
 
 .. _EFM32PG-STK3402A Schematics:
-   https://www.silabs.com/documents/public/schematic-files/EFM32PG12-BRD2501A-A01-schematic.pdf
+   https://www.silabs.com/documents/public/schematic-files/BRD2501A-A01-schematic.pdf
 
 .. _EFM32PG Website:
    https://www.silabs.com/products/mcu/32-bit/efm32-pearl-gecko