usb: phy: omap-otg: fix uninitialized pointer

otg_dev->extcon was referenced before otg_dev was initialized. Fix.

Cc: <stable@vger.kernel.org> # v4.3
Fixes: a2fd2423

 ("usb: phy: omap-otg: Replace deprecated API of extcon")
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Felipe Balbi <balbi@ti.com>