NFS/pNFS: Don't call pnfs_free_bucket_lseg() before removing the request

In pnfs_generic_clear_request_commit(), we try calling
pnfs_free_bucket_lseg() before we remove the request from the DS bucket.
That will always fail, since the point is to test for whether or not
that bucket is empty.

Fixes: c84bea59 ("NFS/pNFS: Simplify bucket layout segment reference counting")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>