ARM: dts: i.MX27: Remove clock name from CPU node

Clock name is not needed for "cpufreq-cpu0".

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>