scsi: scsi_debug: Make sdebug_build_parts() respect virtual_gb

If virtual_gb is passed while using num_parts, when creating the
partitions, virtual_gb is not respected.  Set num_sectors using
get_sdebug_capacity() to pull virtual_gb if set.

Link: https://lore.kernel.org/r/20200902211434.9979-3-jpittman@redhat.comAcked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: John Pittman <jpittman@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_debug.c

@@ -5276,7 +5276,7 @@ static void sdebug_build_parts(unsigned char *ramp, unsigned long store_size)
 		sdebug_num_parts = SDEBUG_MAX_PARTS;
 		pr_warn("reducing partitions to %d\n", SDEBUG_MAX_PARTS);
 	}
-	num_sectors = (int)sdebug_store_sectors;
+	num_sectors = (int)get_sdebug_capacity();
 	sectors_per_part = (num_sectors - sdebug_sectors_per)
 			   / sdebug_num_parts;
 	heads_by_sects = sdebug_heads * sdebug_sectors_per;