drivers/sdcard: Add sleep_ms(1) delay in SDCard.readinto sync loop.

So this driver works on faster MCUs (that run this loop fast) with older,
slower SD cards.

Fixes issue #7129.

Signed-off-by: Damien George <damien@micropython.org>

drivers/sdcard/sdcard.py

@@ -176,6 +176,7 @@ class SDCard:
             self.spi.readinto(self.tokenbuf, 0xFF)
             if self.tokenbuf[0] == _TOKEN_DATA:
                 break
+            time.sleep_ms(1)
         else:
             self.cs(1)
             raise OSError("timeout waiting for response")