USB: xhci: fix couple sparse annotations

There is no point in casting to (void *) when setting up xhci->ir_set
as it only makes us lose __iomem annotation and makes sparse unhappy.

OTOH we do need to cast to (void *) when calculating xhci->dba from
offset, but since it is IO memory we need to annotate it as such.

Signed-off-by: Dmitry Torokhov <dtor@vmware.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>