MIPS: lantiq: Return correct value for fpi clock on ar9

Some configurations of AR9 reported the incorrect speed for the fpi bus.
Signed-off-by: NBen Mulvihill <ben.mulvihill@gmail.com>
Signed-off-by: NJohn Crispin <blogic@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11448/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/lantiq/xway/clk.c

@@ -88,8 +88,9 @@ unsigned long ltq_ar9_fpi_hz(void)
 	unsigned long sys = ltq_ar9_sys_hz();
 
 	if (ltq_cgu_r32(CGU_SYS) & BIT(0))
-		return sys;
-	return sys >> 1;
+		return sys / 3;
+	else
+		return sys / 2;
 }
 
 unsigned long ltq_ar9_cpu_hz(void)