clk: imx: clk-composite-8m: add lock to gate/mux

There is a lock to divider in the composite driver, but that's not
enough. lock to gate/mux are also needed to provide exclusive access
to the register.

Fixes: d3ff9728 ("clk: imx: Add imx composite clock")
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>