Add SDIO pin definitions to the Maple RET6 variant

It was missing, but needed since that variant (RET6) includes the SDIO peripheral, so the files are included in the compilation.

STM32F1/variants/maple_ret6/board/board.h

@@ -102,6 +102,16 @@
 #define BOARD_USB_DISC_DEV      GPIOC
 #define BOARD_USB_DISC_BIT      12
 
+/*
+ * SDIO Pins
+ */
+#define BOARD_SDIO_D0 			PC8
+#define BOARD_SDIO_D1 			PC9
+#define BOARD_SDIO_D2 			PC10
+#define BOARD_SDIO_D3 			PC11
+#define BOARD_SDIO_CLK 			PC12
+#define BOARD_SDIO_CMD 			PD2
+
 /* Pin aliases: these give the GPIO port/bit for each pin as an
  * enum. These are optional, but recommended. They make it easier to
  * write code using low-level GPIO functionality. */
@@ -117,4 +127,4 @@ enum {
 
 //15 16 17 18 19 20 21 22 23 24 25 26 27 28
 
-//29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45
+//29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45