stm32f7: clk: remove usart1 clock enable from board init

Before clock driver availability it was required to enable usart1 clock
for serial init but now with clock driver is taking care of usart1 clock.

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>

board/st/stm32f746-disco/stm32f746-disco.c

@@ -380,7 +380,6 @@ int board_early_init_f(void)
 	int res;
 
 	res = uart_setup_gpio();
-	clock_setup(USART1_CLOCK_CFG);
 	if (res)
 		return res;