Revert "ARM: dts: imx6qdl-apalis: Avoid underscore in node name"

The STMPE MFD device binding requires the child node to have a fixed
name, i.e. with '_', not '-'. Otherwise the stmpe_adc, stmpe_touchscreen
drivers will not be probed.

Fixes: 56086b5e ("ARM: dts: imx6qdl-apalis: Avoid underscore in node name")
Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>