machine: bump rp2350 CPUFrequency to 150 MHz (#4766)

Leave rp2040 speed bump to 200 MHz for a future change, because it
requires bumping the core voltage as well[0].

[0] https://github.com/raspberrypi/pico-sdk/releases/tag/2.1.1

src/machine/machine_rp2_clocks.go

@@ -10,7 +10,7 @@ import (
 )
 
 func CPUFrequency() uint32 {
-	return 125 * MHz
+	return cpuFreq
 }
 
 // clockIndex identifies a hardware clock