media: ov08x40: Move fwnode_graph_get_next_endpoint() call up

If the bridge has not yet setup the fwnode-graph then
the fwnode_property_read_u32("clock-frequency") call will fail.

Make the fwnode_graph_get_next_endpoint() call the first call in
ov08x40_check_hwcfg() and return -EPROBE_DEFER if it fails.

Tested-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>