dt-bindings: arm: imx: scu: fix naming typo of clk compatible string

There is a typo in binding doc that the name of compatible string of
scu clock should be "fsl,xxx-clk" rather than "fsl,xxx-clock".
In reality, both example and dts using "fsl,xxx-clk", so fixing the doc
is enough.

Cc: devicetree@vger.kernel.org
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Abel Vesa <abel.vesa@nxp.com>