nvmet: remove else at the end of the function

The function nvmet_parse_io_cmd() returns value from
nvmet_file_parse_io_cmd() or nvmet_bdev_parse_io_cmd() based on which
backend is set for the request. Remove the else and just return the
value from nvmet_bdev_parse_io_cmd().

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>