Field PLLState was not initialized in RCC_OscInitStruct.PLL in
function SystemClock_Config().
Value is used in HAL_RCC_OscConfig() regardless of oscillator.
In lucky case value would be 0 RCC_PLL_NONE and nothing would
happen.
If value was incorrect following line would end up in assert:
assert_param(IS_RCC_PLL(RCC_OscInitStruct->PLL.PLLState));
If value was valid but no RCC_PLL_NONE pll could be configured
with some other random values.
Setting PLLState to RCC_PLL_NONE eliminates potential problem.
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