musb: fix warning in include/linux/usb/musb.h

Fix the following build warning by including linux/compat.h:
include/linux/usb/musb.h:110: warning: 'struct device' declared inside
parameter list
include/linux/usb/musb.h:110: warning: its scope is only this definition
or declaration, which is probably not what you want

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>