linux-phytec-ti

usb: musb: honour the return value of dma_map_single()

Since dma_map_single() may fail it is good to actually check the return
code to see if it succeeded.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>