[SCSI] megaraid_sas: Add CFG_CLEARED AEN

The following patch for megaraid_sas adds a missing check for
MR_EVT_CFG_CLEARED in megasas_aen_polling().

Signed-off-by: Adam Radford <aradford@gmail.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>