btrfs: remove redundant counter check at btrfs_truncate_inode_items()

At btrfs_truncate_inode_items(), in the while loop when we decide that we
are going to delete an item, it's pointless to check that 'pending_del_nr'
is non-zero in an else clause because the corresponding if statement is
checking if 'pending_del_nr' has a value of zero. So just remove that
condition from the else clause.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>