Reduce the VD queue depth on detecting the throttling condition.

[mkp: incorporate fix for pointer cast issue reported by the test
robot and Guenter Roeck]

Link: https://lore.kernel.org/r/20220708195020.8323-3-sreekanth.reddy@broadcom.comSigned-off-by: Sreekanth Reddy <sreekanth.reddy@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>