ARM: dts: bcmbca: bcm6878: fix timer node cpu mask flag

The cpu mask flag value should match the number of cpu cores in the
chip. Correct the value to two cpus for BCM6878 dual core SoC.

Fixes: 6bcad714 ("ARM: dts: Add DTS files for bcmbca SoC BCM6878")
Signed-off-by: William Zhang <william.zhang@broadcom.com>
Link: https://lore.kernel.org/r/20220801194754.29492-1-william.zhang@broadcom.com


Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>