cdx: Introduce lock to protect controller ops

Add a mutex lock to prevent race between controller ops initiated by
the bus subsystem and the controller registration/unregistration.

Signed-off-by: Abhijit Gangurde <abhijit.gangurde@amd.com>
Link: https://lore.kernel.org/r/20231017160505.10640-3-abhijit.gangurde@amd.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>