USB: gadget: dwc3: Fix composition switch issue during cable disconnect

USB core will not trigger disconnect interrupt during cable disconnect,
if pullup is not active. This could happen if cable is disconnected
right after enabling tethering option. Due to this, gadget driver will
not inform about disconnect event to userspace. Hence userspace will
not switch to default composition. Fix this issue by calling gadget
driver disconnect if pullup is already disabled during cable disconnect.

CRs-Fixed: 418656
Change-Id: I54e039ae157f804d63a670658eb8767a855f3b9f
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>