staging: lustre: lov: fix dereference of ERR_PTR

If lov_sub_get() fails then it returns the error code in ERR_PTR, but
here we were dereferencing sub without checking if lov_sub_get() has
actually succeeded or not. And on error we can directly return the error
code from lov_io_fault_start() as it return 0 on success and the error
code on error.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/lov/lov_io.c

@@ -729,6 +729,8 @@ static int lov_io_fault_start(const struct lu_env *env,
 	fio = &ios->cis_io->u.ci_fault;
 	lio = cl2lov_io(env, ios);
 	sub = lov_sub_get(env, lio, lov_page_stripe(fio->ft_page));
+	if (IS_ERR(sub))
+		return PTR_ERR(sub);
 	sub->sub_io->u.ci_fault.ft_nob = fio->ft_nob;
 	lov_sub_put(sub);
 	return lov_io_start(env, ios);