power: qpnp-smbcharger: change usb_online from bool to int

Currently, the usb_online property can have three values: -EINVAL, 0,
and 1. This should be declared as an int not a bool.

Fix this by changing the declaration to int.

CRs-Fixed: 767944
Change-Id: I20620325e08267f815892102760ac2b5c5d0dd4e
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>