speakup: Fix var_id_t values and thus keymap

speakup: Fix var_id_t values and thus keymap

commit d97a9d7aea04 ("staging/speakup: Add inflection synth parameter")
introduced a new "inflection" speakup parameter next to "pitch", but
the values of the var_id_t enum are actually used by the keymap tables
so we must not renumber them. The effect was that notably the volume
control shortcut (speakup-1 or 2) was actually changing the inflection.

This moves the INFLECTION value at the end of the var_id_t enum to
fix back the enum values. This also adds a warning about it.

Fixes: d97a9d7aea04 ("staging/speakup: Add inflection synth parameter")
Cc: stable@vger.kernel.org
Reported-by: Kirk Reiser <kirk@reisers.ca>
Reported-by: Gregory Nowak <greg@gregn.net>
Tested-by: Gregory Nowak <greg@gregn.net>
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Link: https://lore.kernel.org/r/20201012160646.qmdo4eqtj24hpch4@function
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>