Blackfin: bf537-stamp: fix I2C board defines

The previous merge for cleaning up the I2C driver incorrectly reverted the
CFG_xxx rename for some of the I2C defines.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Heiko Schocher <hs@denx.de>

include/configs/bf537-stamp.h

@@ -308,8 +308,8 @@
  */
 #define CONFIG_HARD_I2C		1
 #define CONFIG_BFIN_TWI_I2C	1
-#define CFG_I2C_SPEED		50000
-#define CFG_I2C_SLAVE		0
+#define CONFIG_SYS_I2C_SPEED	50000
+#define CONFIG_SYS_I2C_SLAVE	0
 
 #define CONFIG_EBIU_SDRRC_VAL  0x306
 #define CONFIG_EBIU_SDGCTL_VAL 0x91114d