nfsd: fix compound state allocation error handling

Move the cstate_alloc call so that if it fails, the response is setup to
encode the NFS error. The out label now means that the
nfsd4_compound_state has not been allocated.

Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>