ipq40xx: fix DTS warning in qcom-ipq4019-cm520-79f.dts

ipq40xx: fix DTS warning in qcom-ipq4019-cm520-79f.dts

.dts:121.4-14: Warning (reg_format): /led_spi/led_gpio@0:reg: \
	property has invalid length (4 bytes) (#address-cells == 1, #size-cells == 1)
.dtb: Warning (pci_device_bus_num): Failed prerequisite 'reg_format'
.dtb: Warning (i2c_bus_reg): Failed prerequisite 'reg_format'
.dtb: Warning (spi_bus_reg): Failed prerequisite 'reg_format'
.dts:119.24-126.5: Warning (avoid_default_addr_size): /led_spi/led_gpio@0: \
	Relying on default #size-cells value

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>