ARM: mxs: Do not search for "fsl,clkctrl"

The "fsl,clkctrl" compatible string is not documented.

It is used only to find the base address of the clock controller.

Instead of searching for an undocumented compatible string, search
for "fsl,imx23-clkctrl" and "fsl,imx28-clkctrl".

Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>