msm: pcie: mask the aggregated interrupt status register

Aggregated interrupts that are configured to be masked should
not be reported in the interrupt handler. Thus, mask the status
value being read in the interrupt handler to filter them out.

Change-Id: I6b563955309795ac2b68c2527cbd763f9300a029
Signed-off-by: Tony Truong <truong@codeaurora.org>