usb: gadget: aspeed: fixup vhub port irq handling

This is a follow-on patch for commit a23be4ed ("usb: gadget: aspeed:
improve vhub port irq handling"): for_each_set_bit() is replaced with
simple for() loop because for() loop runs faster on ASPEED BMC.

Signed-off-by: Tao Ren <rentao.bupt@gmail.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>