linux-phytec-fsl

drbd: Replace vnr_to_mdev() with conn_peer_device()

The new function returns a peer device, which allows us to eliminate a few
instances of first_peer_device().

Signed-off-by: Andreas Gruenbacher <agruen@linbit.com>
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>