The write to the status register is really an ACK for the HW,
and should be treated as such by the driver. Let's move it to the
irq_ack() callback, which will prevent people from moving it around
in order to paper over other bugs.

Fixes: 8c934095 ("PCI: dwc: Clear MSI interrupt status after it is handled,
not before")
Fixes: 7c5925af ("PCI: dwc: Move MSI IRQs allocation to IRQ domains
hierarchical API")
Link: https://lore.kernel.org/linux-pci/20181113225734.8026-1-marc.zyngier@arm.com/Reported-by: NTrent Piepho <tpiepho@impinj.com>
Tested-by: NNiklas Cassel <niklas.cassel@linaro.org>
Tested-by: NGustavo Pimentel <gustavo.pimentel@synopsys.com>
Tested-by: NStanimir Varbanov <svarbanov@mm-sol.com>
Signed-off-by: NMarc Zyngier <marc.zyngier@arm.com>
[lorenzo.pieralisi@arm.com: updated commit log]
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: stable@vger.kernel.org