counter: linux/counter.h: fix Excess kernel-doc description warning

Remove the @priv: line to prevent the kernel-doc warning:

include/linux/counter.h:400: warning: Excess struct member 'priv' description in 'counter_device'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Fixes: f2ee4759 ("counter: remove old and now unused registration API")
Link: https://lore.kernel.org/r/20231223050511.13849-1-rdunlap@infradead.org


Signed-off-by: William Breathitt Gray <william.gray@linaro.org>