linux-wandboard

usb: musb: dsps: document dt bindings properly

DT bindings normally use '-' (hyphens) instead of '_' (underscore),
driver has it the proper way, but binding documentation does not
reflect it, fix it.

Signed-off-by: Afzal Mohammed <afzal@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>