lightnvm: remove unused rq parameter of nvme_nvm_rqtocmd() to kill warning

With gcc 4.1.2:

    drivers/nvme/host/lightnvm.c: In function ‘nvme_nvm_submit_io’:
    drivers/nvme/host/lightnvm.c:498: warning: ‘rq’ is used uninitialized in this function

Indeed, since commit 2e13f33a ("lightnvm: create cmd before
allocating request"), the request is passed to nvme_nvm_rqtocmd() before
it is allocated.

Fortunately, as of commit 91276162 ("lightnvm: refactor end_io
functions for sync"), nvme_nvm_rqtocmd () no longer uses the passed
request, so this warning is a false positive.

Drop the unused parameter to clean up the code and kill the warning.

Fixes: 2e13f33a ("lightnvm: create cmd before allocating request")
Fixes: 91276162

 ("lightnvm: refactor end_io functions for sync")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Jens Axboe <axboe@fb.com>