media: platform: xilinx: fix error return code of xvip_graph_init()

When the list of xdev->notifier.asd_list is empty, no error return code
of xvip_graph_init() is assigned.
To fix this bug, ret is assigned with -ENOENT as error return code.

Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Reviewed-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>