As described in
Documentation/devicetree/bindings/input/touchscreen/stmpe.txt there is
no 'reg' property under stmpe_touchscreen, so remove it to fix the
following build warning with W=1:

arch/arm/boot/dts/tegra30-apalis-eval.dtb:
Warning (unit_address_vs_reg): Node
/i2c@7000d000/stmpe811@41/stmpe_touchscreen has a reg or ranges
property, but no unit name

Similar to commit 89277e8e ("ARM: dts: imx6qdl-apalis: Remove
unneeded reg property").
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>