leds: lm3692x: Handle failure to probe the regulator

leds: lm3692x: Handle failure to probe the regulator

BugLink: https://bugs.launchpad.net/bugs/1860816
[ Upstream commit 396128d2ffcba6e1954cfdc9a89293ff79cbfd7c ]

Instead use devm_regulator_get_optional since the regulator
is optional and check for errors.

Signed-off-by: Guido Günther <agx@sigxcpu.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Reviewed-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>