bhyve: Map the right BAR in init_msix_table()

The PBA and MSI-X table can reside in different BARs.

Reported by: Andy Fiddaman <andy@omniosce.org>
Reviewed by: jhb
Fixes: 7fa233534736 ("bhyve: Map the MSI-X table unconditionally for passthrough")
Sponsored by: The FreeBSD Foundation

(cherry picked from commit 76b45e688ae84a701f52039c4d0abf8e21a3f59c)