arm: Fix to mistake clean the memory space

In currently, when __bss_start is equal to __bss_end__,
The bss loop will clear all the things in memory space.

But just only when __bss_end__ greater than __bss_start__,
we do the clear bss section operation.

Signed-off-by: Zhong Hongbo <bocui107@gmail.com>
Acked-by: Andreas Bießmann <andreas.devel@googlemail.com>
diff --git a/arch/arm/cpu/pxa/start.S b/arch/arm/cpu/pxa/start.S
index ba0de8f..33c73f6 100644
--- a/arch/arm/cpu/pxa/start.S
+++ b/arch/arm/cpu/pxa/start.S
@@ -258,10 +258,12 @@
 	add	r1, r1, r4
 	mov	r2, #0x00000000		/* clear			    */
 
-clbss_l:str	r2, [r0]		/* clear loop...		    */
+clbss_l:cmp	r0, r1			/* clear loop... */
+	bhs	clbss_e			/* if reached end of bss, exit */
+	str	r2, [r0]
 	add	r0, r0, #4
-	cmp	r0, r1
-	bne	clbss_l
+	b	clbss_l
+clbss_e:
 #endif	/* #ifndef CONFIG_SPL_BUILD */
 
 /*