i2c: mux: Fix channel node leak on adapter add failure

i2c_mux_add_adapter() takes a reference to the Device Tree channel node
before registering the new adapter. If adapter registration fails, the
error path frees the private data without dropping that reference.

Release the channel node before freeing the private data.

Fixes: bc45449b1444 ("i2c/of: Automatically populate i2c mux busses from device tree data.")
Signed-off-by: Ahmad Byagowi <ahmadexp@gmail.com>
Cc: <stable@vger.kernel.org> # v3.5+
Acked-by: Peter Rosin <peda@lysator.liu.se>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://patch.msgid.link/b3e46bbee781b3cb4029aca9a71316cc5e36dc17.1787502619.git.ahmadexp@gmail.com