usb: musb-new: Fix improper musb host pointer

When MUSB is operating in peripheral mode, probe registering
musb core using musb_register which intern return int value
for validation. so there is no scope to preserve struct musb
pointer but the same can be used in .remove musb_stop.
So fix this by return musb_register with struct musb pointer.

Cc: Igor Grinberg <grinberg@compulab.co.il>
Cc: Purna Chandra Mandal <purna.mandal@microchip.com>
Tested-by: Chen-Yu Tsai <wens@csie.org> # A33-OlinuXino
Tested-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>