NFSD: restore EINVAL error translation in nfsd_commit()

commit 555dbf1a ("nfsd: Replace use of rwsem with errseq_t")
incidentally broke translation of -EINVAL to nfserr_notsupp.
The patch restores that.

Found by Linux Verification Center (linuxtesting.org) with SVACE.
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Fixes: 555dbf1a ("nfsd: Replace use of rwsem with errseq_t")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/vfs.c

@@ -1173,6 +1173,7 @@ nfsd_commit(struct svc_rqst *rqstp, struct svc_fh *fhp, u64 offset,
 			nfsd_copy_write_verifier(verf, nn);
 			err2 = filemap_check_wb_err(nf->nf_file->f_mapping,
 						    since);
+			err = nfserrno(err2);
 			break;
 		case -EINVAL:
 			err = nfserr_notsupp;
@@ -1180,8 +1181,8 @@ nfsd_commit(struct svc_rqst *rqstp, struct svc_fh *fhp, u64 offset,
 		default:
 			nfsd_reset_write_verifier(nn);
 			trace_nfsd_writeverf_reset(nn, rqstp, err2);
-		}
 			err = nfserrno(err2);
+		}
 	} else
 		nfsd_copy_write_verifier(verf, nn);