board: nucleo_f429zi: fix wrong comment

the clock is 168MHz instead of 180MHz.

Signed-off-by: Jun Li <jun.r.li@intel.com>
diff --git a/boards/arm/nucleo_f429zi/nucleo_f429zi_defconfig b/boards/arm/nucleo_f429zi/nucleo_f429zi_defconfig
index 3bf37f5..dac4668 100644
--- a/boards/arm/nucleo_f429zi/nucleo_f429zi_defconfig
+++ b/boards/arm/nucleo_f429zi/nucleo_f429zi_defconfig
@@ -31,7 +31,7 @@
 # however, the board does not have an external oscillator, so just use
 # the 8MHz clock signal coming from integrated STLink
 CONFIG_CLOCK_STM32_HSE_BYPASS=y
-# produce 180MHz clock at PLL output
+# produce 168MHz clock at PLL output
 CONFIG_CLOCK_STM32_PLL_M_DIVISOR=8
 CONFIG_CLOCK_STM32_PLL_N_MULTIPLIER=336
 CONFIG_CLOCK_STM32_PLL_P_DIVISOR=2