ehci: simplify ehci_state_executing

ehci: simplify ehci_state_executing

ehci_state_executing does not need to check for p->usb_status == USB_RET_ASYNC
or USB_RET_PROCERR, since ehci_execute_complete already does a similar check
and will trigger an assert if either value is encountered.

USB_RET_ASYNC should never be the packet status when execute_complete runs
for obvious reasons, and USB_RET_PROCERR is only used by ehci_state_execute /
ehci_execute not by ehci_state_executing / ehci_execute_complete.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>