The I/O port space is byte addressable, even for word and long accesses.

An example is the VMware svga card, which has long ports on offsets 0,
1, and 2.

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>