Call cpu_relax() while waiting for the current blk-mq polling instance to
complete.

Link: https://lore.kernel.org/r/20210901152542.27866-1-sreekanth.reddy@broadcom.comReviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Sreekanth Reddy <sreekanth.reddy@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>