nfs_clvnops.c: Add an initialization mistakenly removed

Commit e4c7b2b mistakenly removed an initialization of "newvp",
which could result in crashes.

This patch puts the initialization back in.

Reported by:	cy
Tested by:	cy
Fixes:	e4c7b2b ("nfsv4: Add support to NFSv4 for named attributes")

Author: Rick Macklem

sys/fs/nfsclient/nfs_clvnops.c

@@ -1421,6 +1421,7 @@ nfs_lookup(struct vop_lookup_args *ap)
 	NFSUNLOCKMNT(nmp);
 #endif
 
+	newvp = NULLVP;
 	NFSINCRGLOBAL(nfsstatsv1.lookupcache_misses);
 	nanouptime(&ts);
 	error = nfsrpc_lookup(dvp, cnp->cn_nameptr, cnp->cn_namelen,