commit 3e10a2ce98 ("usb: dwc3: add hsphy_interface
property") introduced a possible NULL pointer
dereference because dwc->hsphy_interface can be
NULL.
In order to fix it, all we have to do is guard
strncmp() against a NULL argument.
Fixes: 3e10a2ce98 ("usb: dwc3: add hsphy_interface property")
Tested-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>