可以呼叫 Set PLL frequency,会反回pll设定频率
/**
* @brief Set PLL frequency
* @param[in] u32PllClkSrc is PLL clock source. Including :
* - \ref CLK_PLLCTL_PLLSRC_HXT
* - \ref CLK_PLLCTL_PLLSRC_HIRC
* @param[in] u32PllFreq is PLL frequency.
* @return PLL frequency
* @Details This function is used to configure PLLCTL register to set specified PLL frequency. \n
* The register write-protection function should be disabled before using this function.
*/
uint32_t CLK_EnablePLL(uint32_t u32PllClkSrc, uint32_t u32PllFreq)