board/asus/tinker: rename label linux-next to linux in extlinux.conf

We're not using next branch so let's rename label linux-next to linux.

Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

board/asus/tinker/extlinux.conf

@@ -1,4 +1,4 @@
-label Tinker linux-next
+label Tinker linux
   kernel /boot/uImage
   devicetree /boot/rk3288-tinker.dtb
   append console=ttyS2,115200n8 root=/dev/mmcblk0p1 rootwait