Fix 24 MHz speed on Teensy 4.0

teensy4/clockspeed.c

@@ -153,8 +153,9 @@ uint32_t set_arm_clock(uint32_t frequency)
 		CCM_CBCDR = cbcdr;
 	}
 
-	cbcdr &= ~CCM_CBCDR_PERIPH_CLK_SEL;
-	CCM_CBCDR = cbcdr;
+	//cbcdr &= ~CCM_CBCDR_PERIPH_CLK_SEL;
+	//CCM_CBCDR = cbcdr;  // why does this not work at 24 MHz?
+	CCM_CBCDR &= ~CCM_CBCDR_PERIPH_CLK_SEL;
 	while (CCM_CDHIPR & CCM_CDHIPR_PERIPH_CLK_SEL_BUSY) ; // wait
 
 	F_CPU_ACTUAL = frequency;