usb: musb: Fix host mode error -71 regression

Commit 467d5c98 ("usb: musb: Implement session bit based runtime PM for
musb-core") started implementing musb generic runtime PM support by
introducing devctl register session bit based state control.

This caused a regression where if a USB mass storage device is connected
to a USB hub, we can get:

usb 1-1: reset high-speed USB device number 2 using musb-hdrc
usb 1-1: device descriptor read/64, error -71
usb 1-1.1: new high-speed USB device number 4 using musb-hdrc

This is because before the USB storage device is connected, musb is
in OTG_STATE_A_SUSPEND. And we currently only set need_finish_resume
in musb_stage0_irq() and the related code calling finish_resume_work
in musb_resume() and musb_runtime_resume() never gets called.

To fix the issue, we can call schedule_delayed_work() directly in
musb_stage0_irq() to have finish_resume_work run.

And we should no longer never get interrupts when when suspended.
We have changed musb to no longer need pm_runtime_irqsafe().
The need_finish_resume flag was added in commit 9298b4aa ("usb:
musb: fix device hotplug behind hub") and no longer applies as far
as I can tell. So let's just remove the earlier code that no longer
is needed.

Fixes: 467d5c98 ("usb: musb: Implement session bit based runtime PM for musb-core")
Reported-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Bin Liu <b-liu@ti.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>