nfsd: get rid of unused function definition

commit 557ce264
"nfsd41: replace page based DRC with buffer based DRC"
have remove unused nfsd4_set_statp, but miss the function definition.

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>