greybus: make op_cycle atomic (again)

There's no need to protect updating a connections operation id cycle
counter with the operations spinlock.   That spinlock protects
connection lists, which do not interact with the cycle counter.
All that we require is that it gets updated atomically, and we
can express that requirement in its type.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>