Avoid that gcc 7 reports the following warning when building with W=1:

warning: this statement may fall through [-Wimplicit-fallthrough=]
Signed-off-by: NBart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: NDennis Dalessandro <dennis.dalessandro@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: NDoug Ledford <dledford@redhat.com>