nfsd: fix null dereference on error path

We're forgetting to check the return value from groups_alloc().

Signed-off-by: J. Bruce Fields <[e-mail]>

fs/nfsd/auth.c

···
 		new->fsuid = exp->ex_anon_uid;
 		new->fsgid = exp->ex_anon_gid;
 		gi = groups_alloc(0);
+		if (!gi)
+			goto oom;
 	} else if (flags & NFSEXP_ROOTSQUASH) {
 		if (!new->fsuid)
 			new->fsuid = exp->ex_anon_uid;