cifsd: fix invalid memory access in smb2_write()

Add missing fp initialzation to prevent invalid memory access in
smb2_write().
Reported-by: NCoverity Scan <scan-admin@coverity.com>
Signed-off-by: NNamjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: NSteve French <stfrench@microsoft.com>

fs/cifsd/smb2pdu.c

@@ -6078,7 +6078,7 @@ int smb2_write(struct ksmbd_work *work)
 {
 	struct smb2_write_req *req;
 	struct smb2_write_rsp *rsp, *rsp_org;
-	struct ksmbd_file *fp;
+	struct ksmbd_file *fp = NULL;
 	loff_t offset;
 	size_t length;
 	ssize_t nbytes;