nfsd: work around a gcc-5.1 warning

gcc-5.0 warns about a potential uninitialized variable use in nfsd:

fs/nfsd/nfs4state.c: In function 'nfsd4_process_open2':
fs/nfsd/nfs4state.c:3781:3: warning: 'old_deny_bmap' may be used uninitialized in this function [-Wmaybe-uninitialized]
   reset_union_bmap_deny(old_deny_bmap, stp);
   ^
fs/nfsd/nfs4state.c:3760:16: note: 'old_deny_bmap' was declared here
  unsigned char old_deny_bmap;
                ^

This is a false positive, the code path that is warned about cannot
actually be reached.

This adds an initialization for the variable to make the warning go
away.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4state.c

@@ -3861,7 +3861,7 @@ static __be32
 nfs4_upgrade_open(struct svc_rqst *rqstp, struct nfs4_file *fp, struct svc_fh *cur_fh, struct nfs4_ol_stateid *stp, struct nfsd4_open *open)
 {
 	__be32 status;
-	unsigned char old_deny_bmap;
+	unsigned char old_deny_bmap = stp->st_deny_bmap;
 
 	if (!test_access(open->op_share_access, stp))
 		return nfs4_get_vfs_file(rqstp, fp, cur_fh, stp, open);
@@ -3870,7 +3870,6 @@ nfs4_upgrade_open(struct svc_rqst *rqstp, struct nfs4_file *fp, struct svc_fh *c
 	spin_lock(&fp->fi_lock);
 	status = nfs4_file_check_deny(fp, open->op_share_deny);
 	if (status == nfs_ok) {
-		old_deny_bmap = stp->st_deny_bmap;
 		set_deny(open->op_share_deny, stp);
 		fp->fi_share_deny |=
 				(open->op_share_deny & NFS4_SHARE_DENY_BOTH);