drbd: Fix allyesconfig build, fix recent commit

Globals where prefixed with drbd_, that was missed in the
in #ifdef'nd code when it is built-in.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Fixes: 183ece30 ("drbd: move global variables to drbd namespace and make some static")
Signed-off-by: Jens Axboe <axboe@kernel.dk>