ARM: shmobile: rcar-gen2: Fix error check in regulator quirk

On systems with two regulators, a bogus error message is printed on
success:

    i2c 6-0058: i2c error 2

While adding support for Stout, the number of messages to send was
made variable, but the corresponding return value check of
i2c_transfer() wasn't updated.

Fixes: ff938cd1 ("ARM: shmobile: stout: enable R-Car Gen2 regulator quirk")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>