megaraid_sas : swap whole register in megasas_register_aen

Swap the whole 32 bits we read from the hardware instead of swapping
just the 16bits we care about in place later.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sumit Saxena <sumit.saxena@avagotech.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: James Bottomley <JBottomley@Odin.com>