"tx_ram" points to io memory.  We can't dereference it directly.  Sparse
complains about this: "drivers/usb/musb/cppi_dma.c:1205:25: warning:
dereference of noderef expression"
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>