mx28evk: Remove unneeded 'undef'

There is no need to undef an option that is not enabled by default.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Marek Vasut <marex@denx.de>
Acked-by: Stefano Babic <sbabic@denx.de>

include/configs/mx28evk.h

@@ -214,7 +214,6 @@
 #define CONFIG_SF_DEFAULT_SPEED		24000000
 
 /* (redundant) environemnt in SPI flash */
-#undef CONFIG_ENV_IS_IN_SPI_FLASH
 #ifdef CONFIG_ENV_IS_IN_SPI_FLASH
 #define CONFIG_SYS_REDUNDAND_ENVIRONMENT
 #define CONFIG_ENV_SIZE			0x1000		/* 4KB */