dmaengine: idxd: Clear PRS disable flag when disabling IDXD device

commit 863676fe upstream.

Disabling IDXD device doesn't reset Page Request Service (PRS)
disable flag to its initial value 0. This may cause user confusion
because once PRS is disabled user will see PRS still remains the
previous setting (i.e. disabled) via sysfs interface even after the
device is disabled.

To eliminate user confusion, reset PRS disable flag to ensure that
the PRS flag bit reflects correct state after the device is disabled.

Additionally, simplify the code by setting wq->flags to 0, which clears
all flag bits, including any future additions.

Fixes: f2dc3271

 ("dmaengine: idxd: add per wq PRS disable")
Tested-by: Tony Zhu <tony.zhu@intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/20230712193505.3440752-1-fenghua.yu@intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>