[ARM] Fix div64 implementation.

Our do_div implementation can't correctly handle divisors with the
top bit set.  This cset fixes this up with a minimal change.

arch/arm/lib/div64.S

@@ -30,6 +30,8 @@ ENTRY(do_div64)
 	moveq	lr, #1			@ only divide low bits
 	moveq	nh, onl
 
+	tst	dh, #0x80000000
+	bne	2f
 1:	cmp	nh, dh
 	bls	2f
 	add	lr, lr, #1