ACPIPHP: prevent duplicate slot numbers when no _SUN

Dock bridges generally do not implement _SUN, yet show up as ejectable
slots.  If you have more than one ejectable slot that does not implement
SUN, with the current code you will get duplicate slot numbers.  So, if
there is no _SUN, use the current count of the number of slots found
instead.

Signed-off-by: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Len Brown <len.brown@intel.com>