NFS: Don't print a pNFS error if we aren't using pNFS

We used to check for a valid layout type id before verifying pNFS flags
as an indicator for if we are using pNFS.  This changed in 3132e49e
with the introduction of multiple layout types, since now we are passing
an array of ids instead of just one.  Since then, users have been seeing
a KERN_ERR printk show up whenever mounting NFS v4 without pNFS.  This
patch restores the original behavior of exiting set_pnfs_layoutdriver()
early if we aren't using pNFS.

Fixes 3132e49e ("pnfs: track multiple layout types in fsinfo
structure")
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>