Input: synaptics_i2c - return 0 explicitly on success

error is always zero at the last return in synaptics_i2c_reg_set().
Explicitly return 0 on the success path instead of returning error,
which is the preferred way when there are multiple failure points.

No functional change.

Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
Link: https://patch.msgid.link/20260729171001.260698-4-ekffu200098@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>