usb: musb: Add and use inline function musb_otg_state_string

The musb_otg_state_string() simply calls usb_otg_state_string().
This will make it easier to get rid of the musb->xceiv dependency later.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20221026182657.146630-3-paul@crapouillou.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>