Use peripheral clock to describe the clock signal given to peripherals.

boards/pro_micro_rp2040/examples/pro_micro_rainbow.rs

@@ -80,7 +80,7 @@ fn main() -> ! {
         25,
         pac.PIO0,
         &mut pac.RESETS,
-        clocks.system_clock.freq(),
+        clocks.peripheral_clock.freq(),
         timer.count_down(),
     );
 

rp2040-hal/examples/i2c.rs

@@ -91,7 +91,7 @@ fn main() -> ! {
         scl_pin, // Try `not_an_scl_pin` here
         400.kHz(),
         &mut pac.RESETS,
-        clocks.system_clock,
+        clocks.peripheral_clock,
     );
 
     // Write three bytes to the I²C device with 7-bit address 0x2C