PCI: mobiveil: Fix INTx interrupt clearing in mobiveil_pcie_isr()

The current INTx handling function clears all interrupts after
handling the first pending; this can potentially cause missing INTx
detection. Fix the code to clear only the handled INTx IRQ.

Fixes: 9af6bcb1 ("PCI: mobiveil: Add Mobiveil PCIe Host Bridge IP driver")
Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Minghuan Lian <Minghuan.Lian@nxp.com>
Reviewed-by: Subrahmanya Lingappa <l.subrahmanya@mobiveil.co.in>
Acked-by: Karthikeyan Mitran <m.karthikeyan@mobiveil.co.in>
Tested-by: Karthikeyan Mitran <m.karthikeyan@mobiveil.co.in>