mg_disk: fix enum REQ_OP_ kbuild error

Because we define WRITE/READ as REQ_OPs, we cannot do
switch (rq_data_dir(request))
case READ
....
case WRITE
...

without getting warnings about handling other REQ_OPs.

This just has mq_disk do a if/else like it does in other
places.
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/block/mg_disk.c

@@ -687,15 +687,13 @@ static unsigned int mg_issue_req(struct request *req,
 		unsigned int sect_num,
 		unsigned int sect_cnt)
 {
-	switch (rq_data_dir(req)) {
-	case READ:
+	if (rq_data_dir(req) == READ) {
 		if (mg_out(host, sect_num, sect_cnt, MG_CMD_RD, &mg_read_intr)
 				!= MG_ERR_NONE) {
 			mg_bad_rw_intr(host);
 			return host->error;
 		}
-		break;
-	case WRITE:
+	} else {
 		/* TODO : handler */
 		outb(ATA_NIEN, (unsigned long)host->dev_base + MG_REG_DRV_CTRL);
 		if (mg_out(host, sect_num, sect_cnt, MG_CMD_WR, &mg_write_intr)
@@ -714,7 +712,6 @@ static unsigned int mg_issue_req(struct request *req,
 		mod_timer(&host->timer, jiffies + 3 * HZ);
 		outb(MG_CMD_WR_CONF, (unsigned long)host->dev_base +
 				MG_REG_COMMAND);
-		break;
 	}
 	return MG_ERR_NONE;
 }