usb: musb: fix BULK request on different available endpoints

Fixes co-working issue of usb serial device with usb/net devices while
oter endpoints are free and can be used.This patch implements the policy
that if endpoint resources are available then different BULK request goes
to different endpoint otherwise they are multiplexed to one reserved
endpoint as currently done.

Switch statement case is reordered in musb_giveback() to take care of
bulk request both in multiplex scenario and otherwise.

NAK limit scheme has to be added for multiplexed BULK request scenario
to avoid endpoint starvation due to usb/net devices.

Signed-off-by: Ajay Kumar Gupta <ajay.gupta@ti.com>
Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>