nfsd: fix boolreturn.cocci warnings

fs/nfsd/nfs4state.c:926:8-9: WARNING: return of 0/1 in function 'nfs4_delegation_exists' with return type bool
fs/nfsd/nfs4state.c:2955:9-10: WARNING: return of 0/1 in function 'nfsd4_compound_in_session' with return type bool

 Return statements in functions returning bool should use
 true/false instead of 1/0.
Generated by: scripts/coccinelle/misc/boolreturn.cocci

Fixes: 68b18f52

 ("nfsd: make nfs4_get_existing_delegation less confusing")
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
[bfields: also fix -EAGAIN]
Signed-off-by: J. Bruce Fields <bfields@redhat.com>