Move IRQ workqueue init before request_irq, otherwise host SUSPEND irq
will call schedule_work() and BUG_ON() will fire because musb_irq_work did
not initialised.

We recorded it at
https://blackfin.uclinux.org/gf/project/uclinux-dist/tracker/?action=TrackerItemEdit&tracker_id=141&tracker_item_id=3740

Although the Blackfin port of MUSB is not merged, this bug should be
common for other platform with MUSB
Signed-off-by: Bryan Wu <bryan.wu@analog.com>
Acked-by: Gadiyar, Anand <gadiyar@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>