NFSD: Clean up nfsd_vfs_write()

The RWF_SYNC and !RWF_SYNC arms are now exactly alike except that
the RWF_SYNC arm resets the boot verifier twice in a row. Fix that
redundancy and de-duplicate the code.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/vfs.c

@@ -997,22 +997,11 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf,
 
 	iov_iter_kvec(&iter, WRITE, vec, vlen, *cnt);
 	since = READ_ONCE(file->f_wb_err);
-	if (flags & RWF_SYNC) {
-		if (verf)
-			nfsd_copy_boot_verifier(verf,
-					net_generic(SVC_NET(rqstp),
-					nfsd_net_id));
-		host_err = vfs_iter_write(file, &iter, &pos, flags);
-		if (host_err < 0)
-			nfsd_reset_boot_verifier(net_generic(SVC_NET(rqstp),
-						 nfsd_net_id));
-	} else {
-		if (verf)
-			nfsd_copy_boot_verifier(verf,
-					net_generic(SVC_NET(rqstp),
-					nfsd_net_id));
-		host_err = vfs_iter_write(file, &iter, &pos, flags);
-	}
+	if (verf)
+		nfsd_copy_boot_verifier(verf,
+				net_generic(SVC_NET(rqstp),
+				nfsd_net_id));
+	host_err = vfs_iter_write(file, &iter, &pos, flags);
 	if (host_err < 0) {
 		nfsd_reset_boot_verifier(net_generic(SVC_NET(rqstp),
 					 nfsd_net_id));