Staging: ipack/bridges/tpci200: tpci200_slot_unmap_space() should return 0 if succeed.

tpci200_slot_unmap_space() should return 0 if the operation was properly done. If
not, the caller will think that something wrong happened.

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>