arm64: dts: msm8996: Fix wrong use of GIC_CPU_MASK_SIMPLE()

GICv3 does not have affinity bitmap in the binding for PPI
interrupts. It can be specified using a 4th cell if needed
as documented in the bindings. Clean up the wrong use of the
affinity bitmap using the GIC_CPU_MASK_SIMPLE() macro

Reported-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>