hcd-xhci: check & correct param before using it

usb_xhci_realize() corrects invalid values of property "intrs"
automatically, but the uncorrected value is passed to msi_init(),
which chokes on invalid values.  Delay that until after the
correction.

Resources allocated by usb_xhci_init() are leaked when msi_init()
fails.  Fix by calling it after msi_init().

CC: Gerd Hoffmann <kraxel@redhat.com>
CC: Markus Armbruster <armbru@redhat.com>
CC: Marcel Apfelbaum <marcel@redhat.com>
CC: Michael S. Tsirkin <mst@redhat.com>

Reviewed-by: Markus Armbruster <armbru@redhat.com>
Acked-by: Marcel Apfelbaum <marcel@redhat.com>
Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>