fix(support_rp2040): omit the inline assembler when building for a mismatching target.

Author: yvt

src/r3_support_rp2040/src/usb.rs

@@ -240,6 +240,7 @@ impl usb_device::bus::UsbBus for UsbBus {
         );
 
         // 12 cycle delay
+        #[cfg(target_arch = "arm")]
         unsafe {
             asm!(
                 "b 1f