usb: musb: dsps fix the typo in reg-names of the dma node

I forgot to separete the different names in the reg-names property. This
didn't cause anything to fail because the driver does not use the names
and simply relies on the order of the memory offsets in reg.
This patch fixes this in case it is used later.

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