orangefs: user file_inode() where it is due

Replace wrong use of file->f_path.dentry->d_inode with file_inode(file).
In case orangefs ever finds itself as an overelayfs layer, it would want
to get its own inode and not overlayfs's inode.

DISCLAIMER: I did not test this patch because I do not know how to setup
            an orangefs mount

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Mike Marshall <hubcap@omnibond.com>