btrfs: Remove unused variable mode in btrfs_mount

This is a leftover from 312c89fb ("btrfs: cleanup btrfs_mount()
using btrfs_mount_root()"), the mode was used for opening devices that's
not done here anymore.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/super.c

@@ -1603,14 +1603,10 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
 {
 	struct vfsmount *mnt_root;
 	struct dentry *root;
-	fmode_t mode = FMODE_READ;
 	char *subvol_name = NULL;
 	u64 subvol_objectid = 0;
 	int error = 0;
 
-	if (!(flags & SB_RDONLY))
-		mode |= FMODE_WRITE;
-
 	error = btrfs_parse_subvol_options(data, &subvol_name,
 					&subvol_objectid);
 	if (error) {