extcon: ptn5150: Check current USB mode when probing

When machine boots up, the USB could be already in OTG mode.  In such
case there will be no interrupt coming to ptn5150 device and driver will
report default state of nothing connected.  Detection of USB connection
would happen on first unplug of the cable.

Factor out code for checking current connection mode and call it right
after probe so the existing USB mode will be properly reported.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Vijai Kumar K <vijaikumar.kanagarajan@gmail.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>