usb: musb: omap2430: don't loop indefinitely in interrupt.

When called during resume_irqs, omap2430_musb_set_vbus() is run with
interrupts disabled,  In that case 'jiffies' never changes so the loop
can loop forever.

So impose a maximum loop count and add an 'mdelay' to ensure we wait
a reasonable amount of time for bit to be cleared.

This fixes a hang on resume.

Signed-of-by: NeilBrown <neilb@suse.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>