ARM: dts: i.MX27: Increase "clock-latency" value

i.MX27 CPU can be clocked with a 32 kHz quartz, and not just 32768 Hz,
so increase "clock-latency" value, which will ensure that we use two
clock cycles on frequency change.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>