Fix doc bug

It was referring to the wrong module.  Thanks @jerryneedell!

Author: jepler

shared-bindings/sdcardio/SDCard.c

@@ -62,7 +62,7 @@
 //|       import sdcardio
 //|       import storage
 //|
-//|       sd = adafruit_sdcard.SDCard(board.SPI(), board.SD_CS)
+//|       sd = sdcardio.SDCard(board.SPI(), board.SD_CS)
 //|       vfs = storage.VfsFat(sdcard)
 //|       storage.mount(vfs, '/sd')
 //|       os.listdir('/sd')