MIPS: zboot: Avoid endless loop in clear BSS.

Commit 2ee1503e ("MIPS: zboot: head.S clean up").

After .noreorder removed, clear BSS fall into endless loop. The bne
instruction will add nop to the delay slot at compile time. So a0
register will not increment by 4. Fix it and clear BSS from _edata
to (_end - 1).
Signed-off-by: Jinyang He <hejinyang@loongson.cn>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/boot/compressed/head.S

@@ -26,8 +26,8 @@
 	PTR_LA	a0, _edata
 	PTR_LA	a2, _end
 1:	sw	zero, 0(a0)
+	addiu	a0, a0, 4
 	bne	a2, a0, 1b
-	 addiu	a0, a0, 4
 
 	PTR_LA	a0, (.heap)	     /* heap address */
 	PTR_LA	sp, (.stack + 8192)  /* stack address */