nvmet: use req->cmd directly in file-ns fast path

The function nvmet_file_parse_io_cmd() is called from the fast path. The
local variable to that function cmd is only used once.

Remove the local variable and use req->cmd directly.
Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/io-cmd-file.c

@@ -385,9 +385,7 @@ static void nvmet_file_execute_write_zeroes(struct nvmet_req *req)
 
 u16 nvmet_file_parse_io_cmd(struct nvmet_req *req)
 {
-	struct nvme_command *cmd = req->cmd;
-
-	switch (cmd->common.opcode) {
+	switch (req->cmd->common.opcode) {
 	case nvme_cmd_read:
 	case nvme_cmd_write:
 		req->execute = nvmet_file_execute_rw;