lightnvm: remove unnecessary variables in rrpc

Before vectored I/Os were supported on rrpc, the physical address was
stored as part of the nvm_rqd request. This variable become obsolete
when the ppa_list was introduced. Cleanup this variable.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>