ARMv8: fix bug for flush data cache by set/way

When flush the d$ with set/way instruction, it need calculate the way's
offset = log2(Associativity); but in current uboot's code, it use below
formula to calculate the offset: log2(Associativity * 2 - 1), so finally
it cannot flush data cache properly.
Signed-off-by: NLeo Yan <leoy@marvell.com>

arch/arm/cpu/armv8/cache.S

@@ -31,9 +31,7 @@ ENTRY(__asm_flush_dcache_level)
 	add	x2, x2, #4		/* x2 <- log2(cache line size) */
 	mov	x3, #0x3ff
 	and	x3, x3, x6, lsr #3	/* x3 <- max number of #ways */
-	add	w4, w3, w3
-	sub	w4, w4, 1		/* round up log2(#ways + 1) */
-	clz	w5, w4			/* bit position of #ways */
+	clz	w5, w3			/* bit position of #ways */
 	mov	x4, #0x7fff
 	and	x4, x4, x6, lsr #13	/* x4 <- max number of #sets */
 	/* x12 <- cache level << 1 */