usb: musb: ux500_dma: drop references to U5500

Drop references to deprecated U5500 platform in driver comments.
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Fabio Baltieri <fabio.baltieri@linaro.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/musb/ux500_dma.c

 /*
  * drivers/usb/musb/ux500_dma.c
  *
- * U8500 and U5500 DMA support code
+ * U8500 DMA support code
  *
  * Copyright (C) 2009 STMicroelectronics
  * Copyright (C) 2011 ST-Ericsson SA