lightnvm: pass dma address to hardware rather than pointer

A recent change to lightnvm added code to pass a kernel pointer
to the hardware, which gcc complained about:

drivers/nvme/host/lightnvm.c: In function 'nvme_nvm_rqtocmd':
drivers/nvme/host/lightnvm.c:472:32: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
  c->ph_rw.metadata = cpu_to_le64(rqd->meta_list);

It looks like this has no way of working anyway, so this changes
the code to pass the dma_address instead. This was most likely
what was intended here. Neither of the two are currently ever
written to, so the effect is the same for now.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: a34b1eb78e21 ("lightnvm: enable metadata to be sent to device")
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>