ARM: clk-imx31: Fix the keypad clock name

Fix the keypad clock name, in order to fix the following error:

imx-keypad imx-keypad: failed to get keypad clock
imx-keypad: probe of imx-keypad failed with error -2

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Cc: stable@vger.kernel.org