[SCSI] megaraid_sas: Dont load DevHandle unless FastPath enabled

The following patch for megaraid_sas will fix an issue where the
driver should not be loading the DevHandle unless FastPath is enabled.
 If FastPath was not enabled, this means the hardware raid map
validation failed for some reason, or the map was corrupted, which
could mean the DevHandle could be invalid.

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