i2c: gpio: OF gpio code does not handle defered probe case

i2c: gpio: OF gpio code does not handle defered probe case

When using device-tree and the i2c-gpio driver is called before the
GPIO node has been probed then it needs to correctly defer the probe
instead of returning a permanent error that the gpio numbers are not
valid.

This fixes the following error:
	/i2c@2: invalid GPIO pins, sda=-517/scl=-517

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
(cherry picked from commit 40e7b1153a39e49715a1f75c654d8da66e3638c4)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
(cherry picked from commit 1582407d7809605bc223583d35515829c2ab0071)

Signed-off-by: Damian Hobson-Garcia <dhobsong@igel.co.jp>