rhmaintainers: add block drivers into block layer entry
Bug on drivers/block have been reported to block layer subcomponent for
long time, and actually we have maintained them already, so add the entry
into block layer.
Cc: Jeff Moyer jmoyer@redhat.com
Cc: Vivek Goyal vgoyal@redhat.com
Signed-off-by: Ming Lei ming.lei@redhat.com