usb: xhci-msm-hsic: Disable wakeup properly upon remove

In mxhci_hsic_remove(), the call to device_init_wakeup(dev, 0) only
disables wakeup capability but does not remove the wakeup source. This
could lead to a scenario in which the wakeup source is still active
after the driver is unbound (and the device is still registered). Fix
this by calling device_wakeup_disable() instead.

While here, also remove the unused wakeup_source instance, as this
driver is only using the built-in one that's part of the device struct.

Change-Id: I42a0a6af0c1d58ab5691fe7beaf0143dcfde66cb
Signed-off-by: Jack Pham <jackp@codeaurora.org>