nfsd: "\%s" should be "%s"

Randy says:
> sparse complains about these, as does gcc when used with --pedantic.
> sparse says:
>
> ../fs/nfsd/nfs4state.c:2385:23: warning: unknown escape sequence: '\%'
> ../fs/nfsd/nfs4state.c:2385:23: warning: unknown escape sequence: '\%'
> ../fs/nfsd/nfs4state.c:2388:23: warning: unknown escape sequence: '\%'
> ../fs/nfsd/nfs4state.c:2388:23: warning: unknown escape sequence: '\%'

I'm not sure how this crept in.  Fix it.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>