Don't report requested regulator (via of_regulator_get()) as
non-existent if said regulator is missing from regulator list. Instead
report it as probe deferral to give other, unprobed, drivers a chance
to resolve this.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>