extcon: ptn5150: Do not print error during probe if nothing is attached

The commit 85256f61 ("extcon: ptn5150: Check current USB mode when
probing") reused code for checking CC status register in the probe path
to determine what is initially connected.  However if nothing is
connected, the CC status register will have 0x0 value and print an error
message:

    ptn5150 1-003d: Unknown Port status : 0

This is not an error.  Also any other unknown port status values are not
really errors but unhandled cases.

Fixes: 85256f61 ("extcon: ptn5150: Check current USB mode when probing")
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>