A previous change introduced the atomic use of queue_claimed flag for eq's
and cq's.  The code works fine, but the clearing of the queue_claimed flag
is not atomic.

Change queue_claimed = 0 into xchg(&queue_claimed, 0) to be consistent for
change under atomicity.

Link: https://lore.kernel.org/r/20200501214310.91713-3-jsmart2021@gmail.comReviewed-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NDick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: NJames Smart <jsmart2021@gmail.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>