ARM: imx27.dtsi: fix CSPI PER clock id

CSPI PER clock is per2clk (per2_gate id 60) instead of cspiX_ipg_gate.

Signed-off-by: Gwenhael Goavec-Merou <gwenhael.goavec-merou@armadeus.com>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>