usb: musb: ux500_dma: fix potential NULL dereference error

static checker warning: "drivers/usb/musb/ux500_dma.c:335
ux500_dma_controller_start()
         error: potential NULL dereference 'param_array'."

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>