iio: ch101: Return -ENODEV when get expander GPIO failed

After get expander GPIO failed, the driver should exit probe,
or else it will cause kernel crash in suspend process.

CRs-Fixed: 2880848
Change-Id: Ie06031e0fbc27ea00d646797c86a650748b5ccb6
Signed-off-by: Zhenlin Lian <lianzhenlin@codeaurora.org>