SystemClockHSI_Config() function

Switch the PLL source from HSE to HSI, and select the PLL as SYSCLK source. The system Clock is configured as follows : System Clock source = PLL (HSI) SYSCLK(Hz) = 80000000 HCLK(Hz) = 80000000 AHB Prescaler = 1 APB1 Prescaler = 2 APB2 Prescaler = 1 HSI Frequency(Hz) = 16000000 PLL_M = 16 PLL_N = 160 PLL_P = 2 PLL_Q = 7 PLL_R = 2 VDD(V) = 3.3 Flash Latency(WS) = 5