Fix wrong f_cpu for Nucleo L476RG

Signed-off-by: Frederic.Pillon <[email protected]>

Author: fpistm

boards.txt

@@ -192,7 +192,7 @@ Nucleo_64.menu.board_part_num.NUCLEO_L476RG.node=NODE_L476RG
 Nucleo_64.menu.board_part_num.NUCLEO_L476RG.upload.maximum_size=1048576
 Nucleo_64.menu.board_part_num.NUCLEO_L476RG.upload.maximum_data_size=131072
 Nucleo_64.menu.board_part_num.NUCLEO_L476RG.build.mcu=cortex-m4
-Nucleo_64.menu.board_part_num.NUCLEO_L476RG.build.f_cpu=4000000L
+Nucleo_64.menu.board_part_num.NUCLEO_L476RG.build.f_cpu=80000000L
 Nucleo_64.menu.board_part_num.NUCLEO_L476RG.build.board=NUCLEO_L476RG
 Nucleo_64.menu.board_part_num.NUCLEO_L476RG.build.series=STM32L4xx
 Nucleo_64.menu.board_part_num.NUCLEO_L476RG.build.product_line=STM32L476xx