mmc: card.h: Use NULL instead of 0 for END_FIXUP

Fix the following sparse warnings:

drivers/mmc/card/block.c:2421:9: warning: Using plain integer as NULL pointer

drivers/mmc/core/quirks.c:69:9: warning: Using plain integer as NULL pointer
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <chris@printf.net>

include/linux/mmc/card.h

@@ -353,7 +353,7 @@ struct mmc_fixup {
 #define CID_OEMID_ANY ((unsigned short) -1)
 #define CID_NAME_ANY (NULL)
 
-#define END_FIXUP { 0 }
+#define END_FIXUP { NULL }
 
 #define _FIXUP_EXT(_name, _manfid, _oemid, _rev_start, _rev_end,	\
 		   _cis_vendor, _cis_device,				\