usb: chipidea: udc: refine isr_tr_complete_handler

Matthieu CASTET and Michael Grzeschik mentioned isr_tr_complete_handler
is a bit messy at below:
http://marc.info/?l=linux-usb&m=139047775001152&w=2



This commit creates a new function isr_setup_packet_handler to handle
setup packet, it makes isr_tr_complete_handler easy to read.

This is no functional change at this commit, tested with g_mass_storage
and g_ether.

Cc: Michael Grzeschik <mgr@pengutronix.de>
Cc: Matthieu CASTET <matthieu.castet@parrot.com>
Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>