microblaze: Not to clear r7 after copying DTB to kernel

I can't clear r7 because if I do it I lose information
where DTB come from.

Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/kernel/head.S

@@ -73,7 +73,6 @@ _copy_fdt:
 	bgtid	r3, _copy_fdt /* loop for all entries */
 	addik	r3, r3, -4 /* descrement loop */
 no_fdt_arg:
-	add	r7, r0, r0			/* Clear r7, just to be sure */
 
 #ifdef CONFIG_MMU