musb: process control messages after roothub accepted it

When dealing with non-multipoint devices, if the software root hub code
accepted the message, then we still need to process it normally.  So only
return quickly when the root hub skipped the message or is otherwise in
an error state.

Signed-off-by: Cliff Cai <cliff.cai@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>