usb: cdns3: fix NULL pointer dereference on no platform data

[ Upstream commit 448373d9 ]

Some platforms (e.g. TI) will not have any platform data which will
lead to NULL pointer dereference if we don't check for NULL pdata.

Fixes: 7cea9657

 ("usb: cdns3: add quirk for enable runtime pm by default")
Reported-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Acked-by: Pawel Laszczak <pawell@cadence.com>
Signed-off-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>