include/mmc.h: Fix typo in IS_SD() macro

Signed-off-by: Albin Tonnerre <albin.tonnerre@free-electrons.com>

include/mmc.h

@@ -47,7 +47,7 @@
 
 #define SD_DATA_4BIT	0x00040000
 
-#define IS_SD(x) (mmc->version & SD_VERSION_SD)
+#define IS_SD(x) (x->version & SD_VERSION_SD)
 
 #define MMC_DATA_READ		1
 #define MMC_DATA_WRITE		2