ARM: dts: bcm2835-rpi-zero-w: Fix led polarity

The status "ACT" led on the Raspberry Pi Zero W is on when GPIO 47 is low.

This has been verified on a board and somewhat confirmed by both the GPIO
name ("STATUS_LED_N") and the reduced schematics [1].

[1]: https://www.raspberrypi.org/documentation/hardware/raspberrypi/schematics/rpi_SCH_ZeroW_1p1_reduced.pdf

Fixes: 2c7c040c

 ("ARM: dts: bcm2835: Add Raspberry Pi Zero W")
Signed-off-by: Vincent Stehlé <vincent.stehle@laposte.net>
Cc: Stefan Wahren <stefan.wahren@i2se.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>