btrfs: remove inode_dio_wait() calls when starting reflink operations

When starting a reflink operation we have these calls to inode_dio_wait()
which used to be needed because direct IO writes that don't cross the
i_size boundary did not take the inode's VFS lock, so we could race with
them and end up with ordered extents in target range after calling
btrfs_wait_ordered_range().

However that is not the case anymore, because the inode's VFS lock was
changed from a mutex to a rw semaphore, by commit 9902af79
("parallel lookups: actual switch to rwsem"), and several years later we
started to lock the inode's VFS lock in shared mode for direct IO writes
that don't cross the i_size boundary (commit e9adabb9 ("btrfs: use
shared lock for direct writes within EOF")).

So remove those inode_dio_wait() calls.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>