microblaze: Stop stack clobbering in microblaze-generic.

A typo caused the stack and malloc regions to overlap, which prevented
mem_malloc_init() from returning. This commit makes the memory layout match
the example described in include/configs/microblaze-generic.h

Signed-off-by: Graeme Smecher <graeme.smecher@mail.mcgill.ca>
Signed-off-by: Michal Simek <monstr@monstr.eu>

include/configs/microblaze-generic.h

@@ -146,7 +146,7 @@
 #define	CONFIG_SYS_MALLOC_BASE		(CONFIG_SYS_MONITOR_BASE - CONFIG_SYS_MALLOC_LEN)
 
 /* stack */
-#define	CONFIG_SYS_INIT_SP_OFFSET	CONFIG_SYS_MONITOR_BASE
+#define	CONFIG_SYS_INIT_SP_OFFSET	CONFIG_SYS_MALLOC_BASE
 
 /*#define	RAMENV */
 #define	FLASH