power: qpnp-qg: Fix the sleep_length value in process_suspend

The S3 sleep-length register uses a 0-based offset, hence
add a +1 to get its actual value.

Change-Id: I742a7950f9fc53f17cb6f210f2b7f06ade842013
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>