malta: Switch to using CONFIG_SYS_SDRAM_SIZE

This is the only platform defining and using CONFIG_SYS_MEM_SIZE, switch
to using CONFIG_SYS_SDRAM_SIZE for consistency.

Cc: Paul Burton <paul.burton@mips.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/include/configs/malta.h b/include/configs/malta.h
index c8b230a..98ea860 100644
--- a/include/configs/malta.h
+++ b/include/configs/malta.h
@@ -30,7 +30,7 @@
 #else
 # define CONFIG_SYS_SDRAM_BASE		0x80000000
 #endif
-#define CONFIG_SYS_MEM_SIZE		(256 * 1024 * 1024)
+#define CONFIG_SYS_SDRAM_SIZE		0x10000000	/* 256 MiB */
 
 #define CONFIG_SYS_INIT_SP_OFFSET	0x400000