drivers: w1: fix return check in bit_read for w1-gpio

The driver masked the return value of a pin read operation before
checking the error.
Thus not detecting a potential error and leading to logically
dead code, which was detected by coverity in CID 340853.
Anther instance XORs 1 before returning, resulting in an unexpected
return value;

Signed-off-by: Thomas Stranger <thomas.stranger@outlook.com>