rpi: Update the RPi Zero 2W DT filename

Update the Raspberry Pi Zero 2W device tree file
name to match what landed upstream.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
diff --git a/board/raspberrypi/rpi/rpi.c b/board/raspberrypi/rpi/rpi.c
index fc1fffe..1057ebb 100644
--- a/board/raspberrypi/rpi/rpi.c
+++ b/board/raspberrypi/rpi/rpi.c
@@ -158,7 +158,7 @@
 	},
 	[0x12] = {
 		"Zero 2 W",
-		DTB_DIR "bcm2837-rpi-zero-2.dtb",
+		DTB_DIR "bcm2837-rpi-zero-2-w.dtb",
 		false,
 	},
 	[0x13] = {