scsi: mpt3sas: Fixed memory leaks in driver

While removing Expander devices, we are removing expander device entry
from the list before freeing its child devices. While freeing child
device we are finding its parent device node as NULL and therefore we
are not freeing the child device's allocated data structures.  Updated
the driver to remove the expander device from the list only after
freeing all its child devices.

[mkp: clarified commit message]

Signed-off-by: Sreekanth Reddy <Sreekanth.Reddy@broadcom.com>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>