hpsa: check for a null phys_disk pointer in ioaccel2 path

An oops can occur when submitting ioaccel2 commands when the phys_disk
pointer is NULL in hpsa_scsi_ioaccel_raid_map.  Happens when there are
configuration changes during I/O operations.

If the phys_disk pointer is NULL, send the command down the RAID path.
Reviewed-by: Mahesh Rajashekhara <mahesh.rajashekhara@microsemi.com>
Reviewed-by: Justin Lindley <justin.lindley@microsemi.com>
Reviewed-by: Scott Teel <scott.teel@microsemi.com>
Reviewed-by: Kevin Barnett <kevin.barnett@microsemi.com>
Reviewed-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Signed-off-by: Don Brace <don.brace@microsemi.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/hpsa.c

@@ -4981,6 +4981,8 @@ static int hpsa_scsi_ioaccel_raid_map(struct ctlr_info *h,
 		return IO_ACCEL_INELIGIBLE;
 
 	c->phys_disk = dev->phys_disk[map_index];
+	if (!c->phys_disk)
+		return IO_ACCEL_INELIGIBLE;
 
 	disk_handle = dd[map_index].ioaccel_handle;
 	disk_block = le64_to_cpu(map->disk_starting_blk) +