dmaengine: idxd: fix misc interrupt completion

Nikhil reported the misc interrupt handler can sometimes miss handling
the command interrupt when an error interrupt happens near the same time.
Have the irq handling thread continue to process the misc interrupts until
all interrupts are processed. This is a low usage interrupt and is not
expected to handle high volume traffic. Therefore there is no concern of
this thread running for a long time.

Fixes: 0d5c10b4

 ("dmaengine: idxd: add work queue drain support")
Reported-by: Nikhil Rao <nikhil.rao@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/161074755329.2183844.13295528344116907983.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>