clock: stm32f4: Fix range of CLOCK_STM32F4X_PLLN_MULTIPLIER config
clock: stm32f4: Fix range of CLOCK_STM32F4X_PLLN_MULTIPLIER config

The PLLN multiplier can range between 50 and 432 on all STM32F4, except
on the STM32F401 where the lower bound is restricted to 192.

Fix the range property and the help text to reflect this reality.

Change-Id: I7b93e84b321f7869aaf611287344cd3e25c893c8
Signed-off-by: Florian Vaussard <ef1e2bd37ca89620283a38ee0519838a257cab3b@heig-vd.ch>

fbsder/zephyr,fbsder/zephyr,fbsder/zephyr,fbsder/zephyr,fbsder/zephyr