This is used by the detect callback but never initialized.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

This changes the MUSB support from the original Kernel state to
be usable with barebox. Tested on a custom board and the Beaglebone
Black. The host port on the Beaglebone works, the OTG port works
in device mode, but not yet in host mode.

Based on the initial MUSB port from Rolf Evers Fischer.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>