ARM: dts: imx6qdl-colibri: Remove unneeded reg property

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/imx6dl-colibri-eval-v3.dtb: Warning (unit_address_vs_reg): Node /soc/aips-bus@2100000/i2c@21a4000/stmpe811@41/stmpe_touchscreen has a reg or ranges property, but no unit name

Cc: Sanchayan Maity <maitysanchayan@gmail.com>
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Acked-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>