musb_host: refactor musb_save_toggle() (take 2)

Refactor musb_save_toggle() as follows:

 - replace 'struct musb_hw_ep *ep' parameter by 'struct
   musb_qh *qh' to avoid re-calculating this value 

 - move usb_settogle() call out of the *if* operator.

This is a net minor shrink of source and object code.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>