Fix the copy paste error on the electrodes_rx value set code which will
cause the electrodes_rx value be always set to the value of electrodes_y.

Reported-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Dudley Du <dudl@cypress.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>