Input: imx_keypad - fix missing clk conversions

commit a1e636e6 (Input: imx_keypad - use clk_prepare_enable/
clk_disable_unprepare()) missed to update clk_enable/clk_disable
in imx_keypad_probe().

Fix it so that we do not get clk warnings at boot.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>