led: Mark device instance with DM_FLAG_PROBE_AFTER_BIND

Calling device_probe() from uclass .post_bind() callback has all kinds
of odd side-effects, e.g. device instances not being available just yet.
Make use of the DM_FLAG_PROBE_AFTER_BIND instead, mark device instances
which need to be probe()d in order to configure the LED default state
with this flag and let the DM core do the device_probe() at the right
time instead.

Fixes: 72675b06 ("led: Configure LED default-state on boot")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>
Cc: Sean Anderson <seanga2@gmail.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Steven Lawrance <steven.lawrance@softathome.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
Tested-by: Patrice Chotard <patrice.chotard@foss.st.com>