usb: musb: ux500: harden checks for platform data

In its current state, the ux500-musb driver uses platform data pointers
blindly with no prior checking. If no platform data pointer is passed
this will Oops the kernel. In this patch we ensure platform data and
board data are present prior to using them.

Cc: linux-usb@vger.kernel.org
Acked-by: Felipe Balbi <balbi@ti.com>
Acked-by: Fabio Baltieri <fabio.baltieri@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>