net: smsc911x: back out silently on probe deferrals

When trying to get a regulator we may get deferred and we see
this noise:

smsc911x 1b800000.ethernet-ebi2 (unnamed net_device) (uninitialized):
   couldn't get regulators -517

Then the driver continues anyway. Which means that the regulator
may not be properly retrieved and reference counted, and may be
switched off in case noone else is using it.

Fix this by returning silently on deferred probe and let the
system work it out.

Cc: Jeremy Linton <jeremy.linton@arm.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>