microblaze: Fix endif macro command

Use correct name in endif comment.
Signed-off-by: NMichal Simek <michal.simek@xilinx.com>

arch/microblaze/cpu/start.S

@@ -129,7 +129,7 @@ _start:
 	sh	r7, r0, r8
 	rsubi	r8, r10, 0x26
 	sh	r6, r0, r8
-#endif /* BUILD_SPL */
+#endif /* CONFIG_SPL_BUILD */
 
 	/* Flush cache before enable cache */
 	addik	r5, r0, 0