修复delay_us差太多的问题

Signed-off-by: huhui <huhui@sharkgulf.com>

Application/bsp/clock.c

@@ -3,8 +3,8 @@
 
 extern uint32_t SystemCoreClock;
 void delay_us(uint32_t us){
-	uint32_t insr_num = (SystemCoreClock /40000000 + 1) * us;// 1000000;
-	while(insr_num-->0);
+	uint32_t insr_num = (SystemCoreClock /1000000) * us * 4;// 1000000;
+	while(insr_num-->0); //have 4 instr
 }
 
 uint32_t get_sys_clock(void){