SMB3: Fix crash in SMB2_open_init due to uninitialized field in compounding path

Ran into an intermittent crash in
	SMB2_open_init+0x2f6/0x970
due to oparms.cifs_sb not being initialized when called from:
	smb2_compound_op+0x45d/0x1690
Zero the whole oparms struct in the compounding path before setting up the
oparms so we don't risk any uninitialized fields.

Fixes: fdef665b ("smb3: fix mode passed in on create for modetosid mount option")
Signed-off-by: Steve French <stfrench@microsoft.com>
Acked-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>

fs/cifs/smb2inode.c

@@ -95,6 +95,7 @@ smb2_compound_op(const unsigned int xid, struct cifs_tcon *tcon,
 		goto finished;
 	}
 
+	memset(&oparms, 0, sizeof(struct cifs_open_parms));
 	oparms.tcon = tcon;
 	oparms.desired_access = desired_access;
 	oparms.disposition = create_disposition;