dt-bindings: input: iqs626a: Redefine trackpad property types

Following a recent refactor of the driver to properly drop unused
device nodes, the driver expects trackpad channel touch thresholds
and ATI base values to be specified under single trackpad channel
child nodes.

This enhancement moves both properties to scalar values as opposed
to arrays, making their types consistent across bindings.

Fixes: a8f1f0dc865c ("dt-bindings: input: Add bindings for Azoteq IQS626A")
Signed-off-by: Jeff LaBundy <jeff@labundy.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/Y9RQcddToBr1rrnJ@nixie71
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>