ARM: dts: BCM5301X: Fix I2C controller interrupt

The I2C interrupt controller line is off by 32 because the datasheet
describes interrupt inputs into the GIC which are for Shared Peripheral
Interrupts and are starting at offset 32. The ARM GIC binding expects
the SPI interrupts to be numbered from 0 relative to the SPI base.

Fixes: bb097e3e ("ARM: dts: BCM5301X: Add I2C support to the DT")
Tested-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>