driver core: dev_get_drvdata: Don't check for NULL dev
There is no point in calling dev_get_drvdata without a valid device.
So checking for dev == NULL is pointless. If such a check is ever
needed - which I doubt - the driver should do it before calling
dev_get_drvdata.
We were returning NULL if dev was NULL, which the caller certainly did
not expect anyway, so that was only delaying the crash if the caller
is not paying attention.