btrfs: relax btrfs_inode::ordered_tree_lock IRQ locking context

btrfs: relax btrfs_inode::ordered_tree_lock IRQ locking context

We used IRQ version of spinlock for ordered_tree_lock, as
btrfs_finish_ordered_extent() can be called in end_bbio_data_write()
which was in IRQ context.

However since we're moving all the btrfs_bio::end_io() calls into task
context, there is no more need to support IRQ context thus we can relax
to regular spin_lock()/spin_unlock() for btrfs_inode::ordered_tree_lock.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>