counter: Stop using dev_get_drvdata() to get the counter device

dev_get_drvdata() returns NULL since commit b56346dd

 ("counter: Use
container_of instead of drvdata to track counter_device") which wrongly
claimed there were no users of drvdata. Convert to container_of() to
fix a null pointer dereference.

Reported-by: Oleksij Rempel <o.rempel@pengutronix.de>
Fixes: b56346dd

 ("counter: Use container_of instead of drvdata to track counter_device")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Tested-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Link: https://lore.kernel.org/all/20220204082556.370348-1-u.kleine-koenig@pengutronix.de/
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Link: https://lore.kernel.org/r/4a14311a3b935b62b33e665a97ecaaf2f078228a.1646957732.git.vilhelm.gray@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>