usb: musb: compress return logic into one line

Simplify return logic to avoid unnecessary variable assignment.

Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Acked-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>