counter: 104-quad-8: Describe member 'lock' in 'quad8'

This adds a kernel-doc comment line describing the 'lock' member of the
'quad8' structure.

Acked-by: Syed Nayyar Waris <syednwaris@gmail.com>
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Link: https://lore.kernel.org/r/43b4acab9e238638c7067dd4a363a42f94c94ccb.1628511445.git.vilhelm.gray@gmail.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>