mtd: mtdswap: remove unused variables 'dev' and 'gd'

This was changed recently (commit e8e3edb95ce6 ("mtd: create per-device
and module-scope debugfs entries")) and some compilers are complaining:

   drivers//mtd/mtdswap.c: In function 'mtdswap_add_debugfs':
>> drivers//mtd/mtdswap.c:1317: warning: unused variable 'dev'

And once we kill 'dev', 'gd' is also unused.

Cc: Mario J. Rugiero <mrugiero@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/mtdswap.c

@@ -1313,9 +1313,6 @@ static const struct file_operations mtdswap_fops = {
 
 static int mtdswap_add_debugfs(struct mtdswap_dev *d)
 {
-	struct gendisk *gd = d->mbd_dev->disk;
-	struct device *dev = disk_to_dev(gd);
-
 	struct dentry *root = d->mtd->dbg.dfs_dir;
 	struct dentry *dent;