clk: fsl-sai: fix memory leak

If the device is removed we don't unregister the composite clock. Fix
that.

Fixes: 9cd10205 ("clk: fsl-sai: new driver")
Signed-off-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20201105192746.19564-2-michael@walle.cc


Signed-off-by: Stephen Boyd <sboyd@kernel.org>