samples: boards: nrfx: Fix setting up of (D)PPI channel endpoints

There is a copy-paste error in this sample code that results
in a function for input events being called for an output pin.
By chance, this has no influence on the behavior of the sample,
as the function returns a register offset that for events and
tasks is the same for a given channel, but obviously the code
is confusing.
This is fixed by replacing the relevant part with more suitable
function calls, to also simplify the code a little.

On the occasion, also a remark is added about no button debouncing
used in the sample, to prevent users from being surprised by its
possible behavior.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>
2 files changed