Fix PowerManagementMode::None

Mode was being set to 2 (PM2_POWERSAVE_MODE), should be
0 (NO_POWERSAVE_MODE). Setting None mode failed with a panic:

85.707099 DEBUG set pm2_sleep_ret = [00, 00, 00, 00]
└─ cyw43::control::{impl#0}::set_iovar_v::{async_fn#0} @ cyw43/src/fmt.rs:127
85.710469 ERROR panicked at 'IOCTL error -29'

src/lib.rs

@@ -198,6 +198,7 @@ impl PowerManagementMode {
     fn mode(&self) -> u32 {
         match self {
             PowerManagementMode::ThroughputThrottling => 1,
+            PowerManagementMode::None => 0,
             _ => 2,
         }
     }