The recent change of -funsigned-char causes additions of negative
numbers to become additions of large positive numbers, leading to wrong
calculations of mouse movement. Change these casts to be explicitly
signed, to take into account negative offsets.

Fixes: 3bc753c0 ("kbuild: treat char as always unsigned")
Signed-off-by: NJason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: NHans de Goede <hdegoede@redhat.com>
Cc: stable@vger.kernel.org
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217211
Link: https://lore.kernel.org/r/20230318133010.1285202-1-Jason@zx2c4.comSigned-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>