staging: r8188eu: only OFDM_index[0] is used

Replace the OFDM_index array in struct odm_rf_cal with a single variable.
Only its first component is used.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220206161809.423031-3-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>