usb: dwc3: Fix compilation (forbidden warning)

This change fix a forbidden warning (for uinitialized variable)
that fails the kernel compilation.

The error happens in the dwc3 driver files, therefore the
compilation error could have be seen only when the USB_DWC3_MSM
is selected in the menuconfig instead of the default one,
USB_CI13XXX_MSM.

Change-Id: I90c38ef10c2973274cbda527b3ca92c807909960
Signed-off-by: Ido Shayevitz <idos@codeaurora.org>