dt-bindings: imx8mm-clock: Fix the file path

Currently the following warning is seen with 'make dt_binding_check':

Documentation/devicetree/bindings/clock/imx8mm-clock.yaml: $id: relative path/filename doesn't match actual path or filename

Fix it by removing the "bindings" directory from the file path.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Link: https://lkml.kernel.org/r/20200326171933.13394-2-festevam@gmail.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>