btrfs: directly grab inode at __btrfs_debug_check_extent_io_range()

btrfs: directly grab inode at __btrfs_debug_check_extent_io_range()

We've tested that we are dealing with io tree that is associated to an
inode (its owner is IO_TREE_INODE_IO), so there's no need to call
btrfs_extent_io_tree_to_inode() in a separate line and we just assign
tree->inode to the local inode variable when we declare it.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>