Input: snvs_pwrkey - drop input_free_device call if input_register_device fails

Current code uses devm_input_allocate_device() so don't explicitly call
input_free_device if input_register_device fails.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>