mx53evk: Remove CONFIG_SYS_I2C_SLAVE definition

According to include/i2c.h:

"/*
 * Many boards/controllers/drivers don't support an I2C slave interface so
 * provide a default slave address for them for use in common code.  A real
 * value for CONFIG_SYS_I2C_SLAVE should be defined for any board which does
 * support a slave interface.
 */
#ifndef	CONFIG_SYS_I2C_SLAVE
#define	CONFIG_SYS_I2C_SLAVE	0xfe
#endif
"

As the mxc_i2c driver does not support slave mode, there is no need
to define CONFIG_SYS_I2C_SLAVE in i.MX board file.

Cc: Jason Liu <r64343@freescale.com>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>

include/configs/mx53evk.h

@@ -55,7 +55,6 @@
 #define CONFIG_I2C_MXC
 #define CONFIG_SYS_I2C_MX53_PORT2       1
 #define CONFIG_SYS_I2C_SPEED            100000
-#define CONFIG_SYS_I2C_SLAVE            0xfe
 
 /* PMIC Configs */
 #define CONFIG_PMIC