Fix SD hangs on certain write sequences (#9)

When the card status is not ready yet (after a successful write tx is
completed) a second DMA is scheduled to read the return code (instead of
manually reading it when it's ready). The current code schedules the DMA
and immediately proceeds to complete the read due to a missing early
return. This results in the IRQ handler being called one extra time and
desyncing the TX sequence, which hangs due to "done" > "total"

It is unclear when this happens, allegedly when the DMA IRQ is
triggered before the card becomes Idle (response is pushed after it
becomes Idle).

src/sd/rp2040_sdio.cpp

@@ -662,6 +662,7 @@ static void rp2040_sdio_irq()
                 channel_config_set_dreq(&dmacfg, pio_get_dreq(SDIO_PIO, SDIO_DATA_SM, false));
                 dma_channel_configure(SDIO_DMA_CHB, &dmacfg,
                     &g_sdio.card_response, &SDIO_PIO->rxf[SDIO_DATA_SM], 1, true);
+                return;
             }
         }
     }