usb: dwc3: Fix NULL pointer exception in dwc3_pci_remove()

In dwc3_pci_quirks() function, gpiod lookup table is only registered for
baytrail SOC. But in dwc3_pci_remove(), we try to unregistered it
without any checks. This leads to NULL pointer de-reference exception in
gpiod_remove_lookup_table() when unloading the module for non baytrail
SOCs. This patch fixes this issue.

Fixes: 5741022c ("usb: dwc3: pci: Add GPIO lookup table on platforms
without ACPI GPIO resources")
Cc: <stable@vger.kernel.org>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>